| 2 ANCIENT AND MEDIEVAL SCHOOLS |
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In the broadest sense the term Atomism
refers to any doctrine that explains complex phenomena in terms of aggregates of
fixed particles or units. This philosophy has found its most successful
application in natural science: according to the atomistic view, the material
universe is composed of minute particles, which are considered to be relatively
simple and immutable and too small to be visible. The multiplicity of visible
forms in nature, then, is based upon differences in these particles and in their
configurations; hence any observable changes must be reduced to changes in these
configurations. |
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Atomism is in essence an analytical
doctrine. It regards observable forms in nature not as intrinsic wholes but as
aggregates. In contrast to holistic theories, which explain the parts in terms
of qualities displayed by the whole, Atomism explains the observable properties
of the whole by those of its components and of their configurations. (see also holism) |
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In order to understand the historical
development of Atomism and, especially, its relation to modern atomic theory, it
is necessary to distinguish between Atomism in the strict sense and other forms
of Atomism. Atomism in the strict sense is characterized by three points: the
atoms are absolutely indivisible, qualitatively identical (i.e.,
distinct only in shape, size, and motion), and combinable with each other
only by juxtaposition. Other forms of Atomism are less strict on these points. |
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Atomism is usually associated with a
"realistic" and mechanistic view of
the world. It is realistic in that atoms are not considered as subjective
constructs of the mind employed for the sake of getting a better grip upon the
phenomena to be explained; instead, atoms exist in actual reality.
By the same token, the mechanistic view of things, which holds that all
observable changes can be reduced to changes of configuration, is not merely a
matter of employing a useful explanatory model; the mechanistic thesis holds,
instead, that all observable changes are caused by motions of the atoms.
Finally, as an analytic doctrine Atomism is opposed to organismic doctrines,
which teach that the nature of a whole cannot be discovered by dividing it into
its component parts and studying each part by itself. |
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The term Atomism is derived from the
Greek word atoma--"things that
cannot be cut or divided." |
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The history of Atomism can be divided
into two more or less distinct periods, one philosophical and the other
scientific, with a transition period between them (from the 17th to the 19th
century). This historical fact justifies the distinction between philosophical
and scientific Atomism. |
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In philosophical Atomism, which is as
old as Greek philosophy, attention was focussed not on the detailed explanation
of all kinds of concrete phenomena but on some basic general aspects of these
phenomena and on the general lines according to which a rational explanation of
these aspects was possible. These basic aspects were the existence in nature of
a manifold of different forms and of continuous change. In what way could these
features be explained? Philosophical Atomism offered a general answer to that
question. It did not, however, strictly confine itself to the general problem of
explaining the possibility of change and multiplicity--not even in ancient Greek
Atomism, for in Greek thought philosophy and science still formed a unity.
Consequently, Atomists also tried to give more detailed explanations of concrete
phenomena, such as evaporation, though these explanations were meant more to
endorse the general doctrine of Atomism than to establish a physical theory in
the modern sense of the word. Such a theory was not yet possible, because a
physical theory must be based upon indirect or direct information about the
concrete properties of the atoms involved, and such information was not then
available. |
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With the development of a scientific atomic
theory, the general philosophical problems gradually disappear into the
background. All attention is focussed on the explanation of concrete phenomena.
The properties of the atoms are determined in direct relationship with the
phenomena to be explained. For this reason the chemical atomic theory of the
19th century supposes that each identified chemical
element has its own specific atoms and that each chemical
compound has its own molecules (fixed
combinations of atoms). What particles act as unchanged and undivided units
depends upon what kind of process is involved. Some phenomena, such as
evaporation, are explained by a process in which the molecules remain unchanged
and identical. In chemical reactions, however, the molecules lose their
identity. Their structures are broken up, and the composing atoms, while
retaining their own identity, are rearranged into new molecules. With nuclear
reactions a new level is reached, on which the atoms themselves are no longer
considered as indivisible: more elementary particles than the atoms appear in
the explanations of nuclear reactions. |
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Whereas classical Atomism spoke mainly
of material atoms (i.e., of particles
of matter), the success of the atomic doctrine encouraged the extension of the
general principles of Atomism to other phenomena, more or less removed from the
original field of application. Rather plausible, for example, was the extension
of Atomism to the phenomena of electricity.
There were reasons to suppose the existence of an elementary charge of
electricity associated with an elementary material particle, the electron (19th
century). A second fruitful extension concerned energetic processes (20th
century). Some experimental data suggested the hypothesis that energy can exist
only in amounts that are whole multiples of an elementary quantity of energy.
Extensions of the idea of an atomic structure to amounts of gravitation and even
to time have been attempted but have not been sufficiently confirmed. |
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More removed from the original field of
application of Atomism is a theory known as Logical
Atomism (developed by the eminent philosopher and logician Bertrand
Russell and by the philosopher of language Ludwig
Wittgenstein), which supposes that a perfect isomorphism exists between
an "atom" of language (i.e., an
atomic proposition) and an atomic fact; i.e.,
that for each atomic fact there is a corresponding atomic proposition. An
atomic proposition is one that asserts that a certain thing has a certain
quality; e.g., "this is
red." An atomic fact is the simplest kind of fact and consists in the
possession of a quality by some individual thing. |
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Another application of Atomism (albeit
in a moot sense) lies in the monadology of the
philosopher-scientist G.W. Leibniz. According to
Leibniz the atoms of Democritus, who provides the paradigm case of ancient Greek
Atomism, were not true unities; possessing size and shape, they still were
divisible in principle. The ultimate constituents of things must, therefore, be
points, said Leibniz--not mathematical but metaphysical points; i.e.,
points of real existence. They are indeed a kind of soul, which he came to
call "monads." |
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In psychology, Atomism is a doctrine
about perception. It holds that what man
perceives is a mosaic of atomic sensations, each independent and unconnected
with any other sensation. According to the early modern Empiricist David
Hume and the pre-World War I father of experimental psychology Wilhelm
Wundt, the fact that man nevertheless experiences an ordered whole formed
from the unordered "atoms" of perception is caused by the mind's
capacity to combine them by "association." |
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In 1927 the Belgian astronomer Georges
Lemaître formulated the hypothesis that the present high degree of
differentiation of matter in space and the complexity of forms displayed by the
various astronomical objects must have resulted from a violent explosion and
subsequent dispersal of an originally highly compressed homogeneous material, a
kind of "primitive atom," containing all of the matter that exists.
From the philosophical viewpoint this hypothesis is interesting. By its attempt
to reduce the manifold to unity it recalls the beginning of Greek philosophy,
which was also inspired by a thesis of the unity of being, propounded by the
Eleatic Parmenides. Even apart from their
respective contexts, there is, of course, a great difference between Lemaître's
and Parmenides' conceptions of the unity of being, for the latter combined the
thesis of the unity of being with that of the immutability of being. (see also big-bang
model) |
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Although it would be wrong to classify
Parmenides among the Atomists, it is nonetheless appropriate that in an
introduction to the diverse forms of Atomism, his conception of reality as just
one being should be mentioned. Parmenides' thesis is not only historically but
also logically the cornerstone of atomistic thought. Any atomic theory can be
interpreted as an attempt to reconcile the thesis of the unity and immutability
of being with the fact that the senses observe multiplicity and change. The
different ways in which the unity and immutability are understood characterize
the different forms of Atomism. |
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As corpuscles
(minute particles), atoms can either be endowed with intrinsic qualities or be
inherently qualityless. |
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The most striking basic differences in
the material world, which lead to a first classification of substances in
nature, are those between solids, liquids, gases, and fire. These differences
are an observed datum that must be accounted for by every scientific theory of
nature. It is, therefore, only natural that one of the first attempts to explain
the phenomena of nature was based upon these differences and proclaimed that
there are four qualitatively different primitive constituents of everything,
namely, the four elements: earth, water, air, and fire (Empedocles,
5th century BC)--a theory that dominated physics and chemistry until the 17th
century. (see also nature,
philosophy of) |
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Although the theory of the four elements
is not necessarily an atomistic theory, it obviously lends itself to
interpretation in atomistic terms, namely, when the elements are conceived as
smallest parts that are immutable. In this case, all observable changes are
reduced to the separation and commingling of the primitive elementary
substances. Thus Parmenides' thesis that being is immutable is maintained,
whereas the absolute unity of being is abandoned. Yet, the fact that the
infinite variety of forms and changes in nature is reduced to just one type of
process between only four elementary kinds of atoms shows its affinity with the
thesis of the unity of all being. |
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Notwithstanding the great disparity
between the theory of the four elements and modern chemistry, it is clear that
modern chemistry with its approximately 100 qualitatively different atoms falls
into the same class of atomic theories as that of Empedocles. There are
differences, of course, but these will be deferred for later discussion. |
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More removed from the original thesis of
Parmenides was the theory of his contemporary Anaxagoras
of Clazomenae, which assumed as many qualitatively different "atoms"
as there are different qualitied substances in nature. Inasmuch as these atoms,
which Anaxagoras called "seeds," were eternal and incorruptible, this
theory still contains an idea borrowed from Parmenides. A special feature of
Anaxagoras' theory was that every substance contains all possible kinds of seeds
and is named after the kind of seed that predominates in it. Since the substance
contains also other kinds of seed, it can change into something else by the
separation of its seeds. |
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Another interesting form of Atomism with
inherently qualitied atoms, also based on the doctrine of the four elements, was
proposed by Plato. On mathematical grounds he
determined the exact forms that the smallest parts of the elements must have.
Fire has the form of a tetrahedron, air of an octahedron, water of an
icosahedron, and earth of a cube. Inasmuch as he characterized the atoms of the
four elements by different mathematical forms, Plato's conception can be
considered as a transition between the qualitative and quantitative types of
Atomism. |
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The most significant system of Atomism
in ancient philosophy was that of Democritus
(5th century BC). Democritus agreed with Parmenides on the impossibility of
qualitative change but did not agree with him on that of quantitative change.
This type of change, he maintained, is subject to mathematical reasoning and
therefore possible. By the same token, Democritus also denied the qualitative
multiplicity of visible forms but accepted a multiplicity based on purely
quantitative differences. In order to reduce the observable qualitative
differences to quantitative differences, Democritus postulated the existence of
invisible atoms, characterized only by quantitative properties: size, shape, and
motion. Observed qualitative changes are based upon changes in the combination
of the atoms, which themselves remain intrinsically unchanged. Thus Democritus
arrived at a position that was defined above as Atomism in the strict sense. In
order to make the motion of atoms possible, this Atomism had to accept the
existence of the void (empty space) as a real
entity in which the atoms could move and rearrange themselves. By accepting the
void and by admitting a plurality of beings, even an infinite number of them,
Democritus seemed to abandon--even more than Empedocles did--the unity of being.
Nevertheless, there are sound reasons to maintain that, in spite of this
doctrine of the void, Democritus' theory remained close to Parmenides' thesis of
the unity of being. For Democritus' atoms were conceived in such a way that
almost no differences can be assigned to them. First of all, there are no
qualitative differences; the atoms differ only in shape and size. Secondly, the
latter difference is characterized by continuity;
there are no privileged shapes and no privileged sizes. All shapes and sizes
exist, but they could be placed in a row in such a manner that there would be no
observable difference between successive shapes and sizes. Thus not even the
differences in shape and size seem to offer any ground explaining why atoms
should be different. By accepting an infinite number of atoms, Democritus
retained as much as possible the principle that being is one.
With respect to the acceptance of the void, it must be stressed that the
void in the eyes of Democritus is more nonbeing than being. Thus even this
acceptance does not seriously contradict the unity of being. |
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Democritus had declared quantitative
differences to be intelligible, because they were subject to mathematical
reasoning. Precisely this relationship between quantitative differences and
mathematics made it impossible for Descartes
(17th century) to think along the atomistic lines of Democritus. If the only
thing that is clearly understandable in matter is mathematical proportions, then
matter and spatial extension are the same--a conclusion that Descartes did not
hesitate to draw. Consequently, he rejected not only the idea of indivisible
atoms but also that of the void. In his eyes the concept "void" is a
contradiction in terms. Where there is space, there is by definition extension
and, therefore, matter. |
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Yet, however strange it may seem in view
of his identification of matter with extension, Descartes offered nonetheless a
fully developed theory of smallest particles. To the questions that arise
immediately as to how these particles are separated and distinct from each
other, Descartes answered that a body or a piece of matter is all of that which
moves together. In the beginning of the world all matter was divided into
particles of equal size. These particles were in constant motion and filled all
of space. As, however, there was no empty space for moving particles to move
into, they could only move by taking the places vacated by other particles that,
however, were themselves in motion. Thus the motion of a single particle
involved the motion of an entire closed chain of particles, called a vortex.
As a result of the original motion, some particles were gradually ground into a
spherical form, and the resulting intermediary space became filled with the
surplus splinters or "grindings." Ultimately, three main types of
particles were formed: (1) the splinter materials, which form the finest matter
and possess the greatest velocity; (2) the spherical particles, which are less
fine and have a smaller velocity; and (3) the biggest particles, which
originated from those original particles that were not subject to grinding and
became united into larger parts. |
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Thus Descartes could construct an atomic
theory without atoms in the classical sense. Although this theory as such has
not been of great value for the scientific atomic theory of modern times, its
general tendency was not without importance. However arbitrarily and
speculatively Descartes may have proceeded in the derivation of the different
kind of corpuscles, he finally arrived at corpuscles characterized by
differences in mass, velocity, amount of motion, etc.--properties that could be
treated mathematically. |
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Most systems of Atomism depict the
action between atoms in terms of collision--i.e.,
as actual contact. In Newton's theory of gravitation, however, action
between bodies is supposed to be action at a distance--which means that the body
in question acts everywhere in space. As its action is the expression of its
existence, it is difficult to confine its existence to the limited space that it
is supposed to occupy according to its precise shape and size. There is,
therefore, no reason for a sharp distinction between occupied and empty space.
Consequently, the mind finds it natural to consider the atoms not as extended
particles but as point-centres of force. This conception was worked out by the
Dalmatian scientist R.G. Boscovich (1711-87),
who attempted to account for all known physical effects in terms of action at a
distance between point-particles, dynamic centres of force. (see also Newton's
law of gravitation) |
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The idea of applying the atomistic
conceptions not only to material but also to psychical phenomena is as old as
Atomism itself. Democritus had spoken of the atoms of the soul. According to the
principles of his doctrine these atoms could differ only quantitatively from
those of the body: they were smoother, rounder, and finer. This made it easy for
them to move into all parts of the body. Basically, however, the atoms of the
soul were no less material than other atoms. |
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In Leibniz's
monadology the situation was quite different.
Leibniz did not first conceive of material atoms and then only later interpret
the soul in terms of these atoms; from the
beginning he conceived his "atoms," the monads, in terms of an analogy
with the soul. A monad is much more a spiritual than a material substance.
Monads have no extension; they are centres of action but not, first of all, in
the physical sense. Each of the monads is gifted with some degree of perception;
each mirrors the universe in its own way. Monads differ from each other,
however, in the degree of perception of which they are capable. |
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By their nature all atomic theories
accept a certain degree of immutability of the atoms. For without any fixed
units no rational analysis of complex phenomena is possible. At least with
respect to the stable factors in the analysis involved, the atoms have to be
considered as immutable. According to Atomism in the strict sense, this
immutability had to be interpreted in an absolute way. |
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The same absolute interpretation
appeared in classical chemistry, although its atomic theory deviated from
Atomism in the strict sense by assuming qualitatively different atoms and by
assuming molecules (rather stable aggregates of atoms). The decisive point,
however, is that molecules were formed by mere juxtaposition of atoms without
any intrinsic change of the qualities of the atoms. Modern atomic theory, in
contrast, gives a less rigid interpretation of the immutability of elementary
particles: the particles that build up an atom do not retain their identity in
an absolute way. |
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In some philosophical atomistic
theories, the immutability of the atoms has been understood in a highly relative
sense. This interpretation arose mainly in the circles of those Aristotelian
philosophers who tried to combine atomistic principles with the principle of Aristotle
that elements changed their nature when entering a chemical compound. The
combination of both principles led to the doctrine known as the minima
naturalia theory, which holds that each kind of substance has its specific minima naturalia, or smallest entities in nature. Minima
naturalia are not absolutely indivisible: they can be divided but then
become minima naturalia of another substance; they change their nature. In
a chemical reaction the minima of the
reagents change into the minima of the
substances that result from the reaction. |
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Atomisms also differ regarding the
number of atoms, whether they occupy a void, and how they relate to one another. |
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As has already been mentioned,
Democritus introduced the hypothesis that the atoms are infinite in number.
Although one may question whether the term infinite has to be taken in its
strict sense, there is no doubt that by using this term Democritus wanted not
merely to express the triviality that, on account of their smallness, there had
to be an enormous quantity of atoms. Democritus also had a strong rational
argument for postulating a strictly infinite quantity of atoms: only thus could
he exclude the existence of atoms that specifically differed from each other. |
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When in modern science the problem of
the number of atoms arises, the situation is quite different from that of the
Greek Atomists. There is now much more detailed information about the properties
of the atoms and of the elementary particles, and there is also in astrophysical
cosmology some information about the universe as
a whole. Consequently, the attempt to calculate the total number of atoms that
exist is not entirely impossible, although it remains a highly speculative
matter. In a time (around 1930) when all chemical atoms were supposed to be
composed of electrons and protons, the pioneering joint-relativity-quantum
astrophysicist A.S. Eddington calculated the
number of these elementary particles to be 2 ×136 × 2256, or
approximately 1079, arguing that, since matter curves space, this is
just the number of particles required barely to close the universe up into a
hypersphere and to fill up all possible existence states. |
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To Democritus the existence of the void
was a necessary element in atomistic theory. Without the void the atoms could
not be separated from each other and they could not move. In the 17th century
Descartes rejected the existence of the void, whereas Newton's
conception of action at a distance was in perfect harmony with the acceptance of
the void and the drawing of a sharp distinction between occupied and nonoccupied
space. |
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The success of the Newtonian law of
gravitation was one of the reasons that atomic theories came to prevail in the
18th century. Even with respect to the phenomena of light, the corpuscular and
hence atomic theory of Newton, which held that light
is made of tiny particles, was adopted almost universally, in spite of Huygens'
brilliant development of the wave hypothesis. (see also corpuscular
theory of light) |
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When in the beginning of the 19th
century the corpuscular theory of light in its turn was abandoned in favour of
the wave theory, the case for the existence of the void had to be reopened, for
the proponents of the wave theory did not think in terms of action at a
distance; the propagation of waves seemed to presuppose, instead, a medium with
not only geometrical properties but with physical ones as well. At first the
physical properties of the medium, the ether,
were described in the language of mechanics; later they were described in that
of the electromagnetic field theory of J.C. Maxwell. Yet, to a certain extent
the old dichotomy between occupied and nonoccupied space continued to exist.
For, according to the ether theory, the atoms moved without difficulty in the
ether, whereas the ether pervaded all physical bodies. (see also corpuscle,
electromagnetic radiation) |
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In contemporary science this dichotomy
has lost its sharpness, owing to the fact that the distinction between material
phenomena, which were supposed to be discontinuous, and the phenomena of light,
which were supposed to be continuous, appears to be only a relative one. In
conclusion it can be claimed that although modern theories still speak of space
and even of "empty" space, this "emptiness" is not absolute:
space has come to be regarded as the seat of the electromagnetic field, and it
certainly is not the void in the sense in which the term was used by Democritus. |
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In most forms of Atomism it is a matter
of principle that any combination of atoms into a greater unity can only be an
aggregate of these atoms. The atoms remain intrinsically unchanged and retain
their identity. The classical atomic theory of chemistry was based upon the same
principle: the union of the atoms into the molecules of a compound was conceived
as a simple juxtaposition. Each chemical formula (e.g.,
H2O, H2SO4, NaCl, etc.) reflects this
principle through the tacit implication that each atom is still an H, O, or S,
etc., even when in combination to form a molecule. (see also chemical
compound ) |
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Chemistry had a twofold reason for
adopting this principle. One reason was an observational, the other a
philosophical one. The fact that some of the properties of a chemical compound
could, by simple juxtaposition, be derived from those of the elements (the
molecular weight, for example, equals the simple sum of the respective atomic
weights) was a strong factual argument in favour of the principle. Many
properties of the components, however, could not be determined in this way. In
fact, most chemical properties of compounds differed considerably from those of
the composing elements. Consequently, the principle of juxtaposition could not
be based on factual data alone. It was in need of a more general support. This
support was offered by the philosophical idea that inspired all Atomism, viz.,
that if complex phenomena cannot be explained in terms of aggregates of more
elementary factors, they cannot be explained at all. |
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For the evaluation of this idea, the
development of the scientific atomic theory is highly interesting, especially
with respect to the interpretation of the concept of an aggregate. Is the only
interpretation of this concept that of an assemblage in which the components
preserve their individuality--like, for instance, a heap of stones? |
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Modern atomic theory offers an answer to
this question. This theory still adheres to the basic principle that a complex
structure has to be explained in terms of aggregates of more elementary factors,
but it interprets the term "aggregate" in such a way that it is not
limited to a mere juxtaposition of the components. In modern theories atomic and
molecular structures are characterized as associations of many interacting
entities that lose their own identity.
The resulting aggregate originates from the converging contributions of all of
its components. Yet, it forms a new entity, which in its turn controls the
behaviour of its components. Instead of mere juxtaposition of components, there
is an internal relationship between them. Or, expressed in another way: in order
to know the properties of the components, one has to study not only the isolated
components but also the structures into which they enter. To a certain extent
modern atomic theory has bridged the gap between atomistic and holistic thought. |
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From the ancient Greeks through the 16th
century, Atomism remained mainly philosophical. |
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It is characteristic of the importance
of Greek philosophy that, already in the
foregoing exposition of the different aspects of Atomism, several Greek
philosophers had to be introduced. Not only the general idea of Atomism but also
the whole spectrum of its different forms originated in ancient Greece. As early
as the 5th century BC Atomism in the strict sense (Leucippus and Democritus) is
found, along with various qualitative forms of Atomism: that of Empedocles,
based on the doctrine of the four elements, and that of Anaxagoras, with as many
qualitatively different atoms as there are different substances. |
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Yet, in spite of its successful start,
Atomism did not gain preeminence in Greek thought. This is mainly because Plato
and Aristotle were not satisfied with the atomistic solution of the problems of
change as a general solution. They refused to reduce the whole of reality,
including man, to a system that knew nothing but moving atoms. Even with respect
to the problems of the material world, Atomism seemed to offer no sufficient
explanation. It did not explain the observable fact that, notwithstanding
continual changes, a total order of specific forms continued to exist. For this
reason Aristotle, with Plato, was more interested in the principle of order than
in that of the material elements. In his own analysis of change, which resulted
in the matter-form doctrine, Aristotle explicitly rejected the thesis of
Democritus that in a chemical reaction the component parts retain their
identity. According to Aristotle, the elements that entered into a composite
with each other did not remain what they were but became a compound. Although
there is some indication that in Aristotle's chemical theory smallest particles
played a role, it was certainly not a very important one. |
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Meanwhile, atomistic ideas remained
known in Greek thought. Their opponents paid much attention to them, and there
were also a few adherents of Democritean Atomism in later times, such as the
Greek hedonist Epicurus (c. 341-279
BC) and the Roman poet Lucretius Carus (c.
95-55 BC) who, through his famous didactic poem De
rerum natura ("On the Nature of Things"), introduced Atomism into
the Latin world. |
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Empedocles had suggested an Atomism with
qualitatively different atoms, based upon the doctrine of the four elements.
Aristotle adopted the latter doctrine but without its atomistic suggestion.
Certain Greek commentators on the works of Aristotle, however, viz., Alexander
of Aphrodisias (2nd century AD), Themistius (4th century AD), and Philoponus
(6th century AD), combined the Aristotelian theory of chemical reactions with
atomistic conceptions. In their systems the atoms were called elachista
("very small" or "smallest"). The choice of this term is
connected with the Aristotelian rejection of the infinite divisibility of
matter. Each substance had its own minimum of magnitude below which it could not
exist. If such a minimum particle were to be divided, then it would become a
minimum of another substance. |
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The Latin commentators on Aristotle
translated the term elachista into its
Latin equivalent minima or also into minima
naturalia; i.e., minima determined by the nature of each substance. In fact,
for most medieval Aristotelians the minima
acquired little more reality than the theoretical limit of divisibility of a
substance; and in their descriptions of physical and chemical processes, they
paid no attention to the minima. With
the Averroists--followers of the Arab Aristotelian Averroës
(1126-98)--an interesting development occurred. Agostino
Nifo (1473-1538), for example, explicitly stated that in a substance the minima
naturalia are present as parts; they
are physical entities that actually play a role in certain physical and chemical
processes. Because the minima had
acquired more physical reality, it then became necessary to know how the
properties of the minima could be
connected with the sensible properties of a substance. Speculations in this
direction were developed by the Italian physician, philosopher, and litterateur Julius
Caesar Scaliger (1484-1558). |
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Modern Atomism arose with the flowering
of science in the present sense of the word. |
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In the history of Atomism the 17th
century occupies a special place for two reasons: it saw the revival of
Democritean Atomism, and it saw the beginning of a scientific
atomic theory. |
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The revival of Democritean Atomism was
the work of the ambiguous Epicureo-Christian thinker Pierre
Gassendi (1592-1655), who made his contemporaries not only better
acquainted with Atomism but also succeeded in divesting it of the materialistic
interpretation with which it was hereditarily infected. This reintroduction of
Democritus was well timed. Because of its quantitative character Democritus'
Atomism invited for its elucidation the application of mathematics and
mechanics, which in the 17th century were sufficiently developed to answer this
invitation. In point of fact, the 17th century was more interested in the
possibilities that Atomism offered for a physical theory than it was in the
philosophical differences between the different atomistic systems. For this
reason it saw, for example, hardly any difference between the systems of
Gassendi and Descartes, although the latter explicitly rejected some of the
fundamentals of Democritus, such as the existence of the void
and the indivisibility of the atoms, as noted above (see Atoms
as sheer extension ). |
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In the case of scientists mainly
interested in the chemical aspects, the same shift of emphasis from
philosophical to scientific considerations can be discerned. According to the
physician and philosopher of nature Daniel Sennert (1572-1637), Democritus'
Atomism and the minima theory really
amounted to the same thing. As far as philosophy was concerned, Sennert was only
interested in the general idea of Atomism; the precise content of an atomic
doctrine in his view ought to be a matter of chemical experimentation. His own
experience as a chemist taught him the specific differences existing between the
atoms. In this respect Sennert continued the minima
tradition. His own contribution to the chemical atomic theory lay in the
clear distinction that he made between elementary atoms and the prima mista, or atoms of chemical compounds. |
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The early modern experimentalist Robert
Boyle (1627-91) followed the same line of thought as Sennert, but he was
much more aware of the discrepancy between Democritus' Atomism and an atomic
theory suitable for chemical purposes. Boyle's solution to this problem was the
thesis that the atoms of Democritus were normally associated into primary
concretions, which did not easily dissociate and which acted as elementary atoms
in the chemical sense. These primary concretions can combine to form compounds
of a higher order, which may be compared to Sennert's prima
mista and to the molecules of modern chemistry. |
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The 17th century had laid the
theoretical foundations for a scientific atomic theory. For its further
development it was in need of better chemical insights, especially concerning
the problem of what substances should be considered as chemical elements. Boyle
had shown conclusively that the traditional four "elements" were
certainly not elementary substances, but at the same time he confessed that he
did not yet see any satisfactory method to determine which substances were true
elements. This method was provided by another of the principal founders of
modern chemistry A.-L. Lavoisier (1743-94): a
chemical element is a substance that cannot be further analyzed by known
chemical methods. |
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John Dalton
(1766-1844), usually regarded as the father of modern atomic theory, applied the
results of Lavoisier's chemical work to atomistic conceptions. When Dalton spoke
of elementary atoms, he did not have a merely theoretical idea in mind but the
chemical elements as determined by Lavoisier. Dalton held that there are as many
different kinds of elementary atoms as there are chemical elements. The atoms of
a certain element are perfectly alike in weight, figure, etc.; and the same
point applies to the atoms of a certain compound. As weight was the decisive
characteristic in Lavoisier's theory, Dalton stressed the importance of
ascertaining the relative weights of atoms and the number of elementary atoms
that constituted one compound "atom." As to the question of the way in
which the atoms are combined in a compound, Dalton conceived this combination as
a simple juxtaposition with each atom under the influence of Newtonian forces of
attraction. The atoms retain their identity through a chemical reaction. In this
one point the founder of the chemical atomic theory did not differ from
Democritus. |
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Until its development in the third
decade of the 20th century, the scientific atomic theory did not differ
philosophically very much from that of Dalton, although at first sight the
difference may appear large. Dalton's atoms were no longer considered to be
immutable and indivisible; new elementary particles sometimes appeared on the
scene; and molecules were no longer seen as a mere juxtaposition of atoms--when
entering into a compound atoms became ions. Yet, these differences were only
accidental; the atoms revealed themselves as composed of more elementary
particles--protons, neutrons, and electrons--but these particles themselves were
considered then as immutable. Thus the general picture remained the same. The
material world was still thought to be composed of smallest particles, which
differed in nature and which in certain definite ways could form relatively
stable structures (atoms). These structures were able to form new combinations (molecules)
by exchanging certain component parts (electrons). The whole process was ruled
by well-known mechanical and electrodynamic laws. |
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In contemporary atomic theory the
differences from Dalton are much more fundamental. The hypothesis of the
existence of immutable elementary particles has
been abandoned: elementary particles can be transformed into radiation and vice
versa. And when they combine into greater units, the particles do not
necessarily preserve their identity; they can be absorbed into a greater whole. |
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It is interesting to note that atomistic
conceptions are not restricted to Western philosophy and science. Examples of
qualitative Atomism, based upon the doctrine of the four elements, are also
found in Indian philosophy. In some Indian
systems the atoms are not absolutely indivisible but only relatively so. In
certain aspects Indian Atomism is, therefore, more related to the minima
doctrine than to the Atomism of Democritus. Indian Atomism has, however, not
developed into a scientific theory. |
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In discussing Atomism, one particular
system, that of Democritus, has been here distinguished as Atomism in the strict
sense because of the fact that in no other system have the foundational issues
of Atomism been so clearly expressed. Atomism in the strict sense is not merely
one of the historical forms of Atomism, one of the many possible scientific
attempts at explaining certain physical phenomena; it is, first of all, a metaphysical
system: it has been presented as the only possible explanation of change and
multiplicity. And as a metaphysic it is rationalistic,
mechanistic, and realistic. |
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It is rationalistic
because it has so much confidence in reason that, in order to explain
observed phenomena, it does not hesitate to postulate the existence of
unobservable atoms: i.e., of things
that are in principle unobservable by the human senses and can be known only by
a process of reasoning. Atomists go even further, for they not only are
convinced of the existence of atoms but they also think it possible to deduce in
a rational way their fundamental properties. Moreover, the description of these
properties in mechanistic terms is not
just a matter of convenience; it is supposed to be the adequate expression of reality.
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This rationalistic and mechanistic
metaphysics is not only characteristic of Democritus' Atomism but also of the
early forms of scientific Atomism. The clearest expression of this metaphysics
is found in Descartes. For Democritus mechanistic concepts are clear and
distinct ideas, so that any further experimental investigation is superfluous.
It should be stressed that the atomistic assumption that the human mind, by mere
reasoning, can know the properties of the atoms is a necessary consequence of
the idea that atoms are not subject to internal change; for the changeless can
never be a subject of experimentation. The great weakness of the mechanistic
concept of immutable atoms was that it forced the analyzing experiments to stop
at the atoms; but this weakness could reveal itself only after, in the course of
the further development of science, the fundamentally experimental character of
human knowledge had become evident. |
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This weakness, in fact, was precisely
one of the reasons why Aristotle rejected the
Atomism of Democritus, viz., that the latter had
postulated atoms that were not subject to change. For Aristotle the very essence
of matter was its being subject to change; hence to him the concept of immutable
atoms was a contradiction in terms. |
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Aristotle's criticism of Atomism was
clearly directed against its mechanistic metaphysics, not against its realism.
This latter characteristic was the target, however, of an attack launched by the
incomparable 18th-century epistemologist Immanuel Kant.
In a famous argument, known as the antinomy of
the continuum, Kant tried to prove that the acceptance of the reality of spatial
extension, the cornerstone of Atomism, led to contradictions. His argument can
be summarized as follows: It is possible to prove that any compound must be
composed of simple things (for if not, there would be nothing but composition).
On the other hand, it also is possible to prove that no material thing can be
simple, for the very reason that a part of an extended being is always extended
and is thus open to division. Hence, every allegedly simple part is at once
simple and nonsimple. Consequently, spatial extension cannot be real. Extension
is therefore not a property of the material world itself; it is a form imposed
upon reality by man's perception. |
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By his argument Kant did not intend to
reject atomic theories as such; he rejected only their realistic pretensions.
Kant was deeply convinced that man had to think
of nature by way of analogy with a mechanism, but he denied that knowledge
construed in such a fashion could reach reality itself. |
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In the 19th century, scientists were, as
a rule, hardly impressed by Kant's attack on the realistic pretensions of human
knowledge. Scientists had already learned to go their own way and no longer
worried about philosophical considerations. Only when an internal crisis in
science itself arose were they prepared to reflect upon their presuppositions.
Such a crisis occurred in the 20th century when science was forced to accept the
relativity of both classical models: the wave
and the particle models. |
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To a certain extent, the problem of
whether a scientific model is nothing but a subjective construct in which the
scientist unites his experience is the same as the problem that Kant had in
mind. One of the differences, however, is that in Kant's time science was still
rather exclusively theory. Its close
connection with praxis (practice, doing) had not yet been discovered. For this
reason the Kantian epistemological (or human knowledge) problem could centre on
such a question as: what guarantee does the knowing
subject have that his "models" of reality reflect reality itself?
Inasmuch as, in an exclusively theoretical science, the only contact that one
has with reality is afforded by means of one's knowledge, the problem seems to
be insoluble. |
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The development of science from a
theoretical to an experimental discipline forces philosophy to view the
epistemological problem in a new way. For in an experimental science man is in a
twofold contact with reality, viz., by his knowledge and by his experimental
praxis. Modern atomic theory is one of the best examples to illustrate this
point. It was this theory that was most directly confronted with the problem of
the realistic value of its models. It could take up this challenge because of
the theory's effectiveness for experimental praxis, which is the final judge of
the realistic value of the theoretical models. It has confirmed the audacious
rational speculations of ancient Atomism; but at the same time it has revealed
that, in order to be really effective, reason is in need of experimental
assistance. |
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In comparing Greek Atomism and modern
atomic theories, it should be recalled that in Greek thought philosophy and
science still formed a unity. Greek Atomism was inspired as much by the desire
to find a solution for the problems of mutability and plurality in nature as by
the desire to provide scientific explanations for specific phenomena. While it
is true that some of the Greek Atomists' ideas can rightly be considered as
precursors of later physics, the main importance of the old atomistic doctrines
for modern science does not lie in these primitive anticipations. Much more
important is the attempt to take seriously the variety and mutability discerned
by sense experience and yet to reconcile it with the thesis of Parmenides about
the unity and the immutability of matter. In its search for universal and
unchangeable laws, modern science is to a great extent inspired by the same idea
as Parmenides, since universal laws presuppose a certain unity in the material
world and unchangeable laws cannot be established without the presupposition
that something unchangeable must be hidden behind all changes. By the same
token, without this latter presupposition experiments would not make any sense
at all. For if the diversity of reactions occurring under different conditions
is to reveal anything, these reactions must be the expression of an immutable
nature. The differences have to indicate something about that which remains the
same. The great achievement of the Greek philosophers
was, therefore, that they took a general view of nature as a whole that made a
scientific attitude possible. To this, both the quantitative and the qualitative
forms of Atomism contributed, the former drawing attention to the mathematical
aspects of the problem, the latter to the observational. |
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A comparison of ancient Greek Atomism
with scientific Atomism merely on the basis of their respective scientific
contents would therefore do a great injustice to Greek Atomism; it would in fact
misjudge its main value. Such a comparison would, however, also take too narrow
a view of modern scientific Atomism. It would imply the philosophical
irrelevance of the latter. It has here been shown, however, that the later
development of the scientific atomic theory has clarified many philosophical
problems that, as basic issues, divided Atomism in the strict sense from other
forms of Atomism. To mention only a few examples: the development of the
scientific atomic theory has deepened man's insights into the relationship
between a whole and its components, into the relative character of ultimate
particles, and into certain fundamental epistemological problems. |
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The success of the atomic theory shows
the value of the idea of Atomism: the explanation of the complex in terms of
aggregates of fixed particles or units. Its history also shows, however, the
inherent danger of this idea, namely, that of absolutism. History has corrected
this absolutism: the unitary factors have to be conceived as ultimate only with
respect to the complex under consideration, and their union into aggregates need
not occur only by way of juxtaposition. (A.G.M.v.M.) |
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