But of the mode of operation of this 'intuition of the mind' there is no criterion. The doctrine of the properties, shapes, motions, etc. of the atoms is a creation of the imagination, suggested by certain analogies from sensible things, but incapable of being verified by the senses, which he regards as the only sure foundations of knowledge.
But even on the supposition that the existence and properties of the atoms had been satisfactorily established, no adequate explanation is offered of their relation to the facts of existence. The same difficulty is encountered at the outset of this as of all other ancient systems of ontology, viz. how to pass from the eternal and immutable forms of the atoms to the variety and transitory nature of sensible objects. This is the very difficulty which Lucretius himself urges against the system of Heraclitus,—
Nam cur tam variae res possint esse requiro,
Ex uno si sunt igni puroque creatae.
The order of Nature now subsisting is declared to be the result of the manifold combination of the atoms through infinite time and space, but the intermediate stages by which this process was effected are assumed rather than investigated. We seem to pass 'per saltum' from the chaos of lifeless elements to the perfect order and manifold life of our system. This wide chasm seems as little capable of being bridged by the help of the atoms of Democritus, as by the watery element of Thales or the fiery element of Heraclitus. But in Lucretius this difficulty is partially concealed, by a poetical element in his conception, really inconsistent with the mechanical materialism on which his philosophy professes to be based.—It is to be observed that while the Greek word ἄτομα implies merely the notion of individual existences, the words used by Lucretius, 'semina,' 'genitalia corpora,' really indicate a creative capacity in these existences. In conceiving their power of carrying on and sustaining the order of Nature, his imagination is thus aided by the analogy of the growth of plants and living beings. A secret faculty in the atoms, distinct from their other properties, is assumed. Thus he says—
At primordia gignundis in rebus oportet
Naturam clandestinam caecamque adhibere.[396]
In his statement of the doctrine of the Clinamen, or slight declension in the motion of the atoms, so as 'to break the chain of fate,' he attributes to them a power analogous to volition in living beings. This doctrine is suggested by the necessity of explaining contingency in Nature and freedom in the movements of sentient beings. We are, as in all attempts to account for creation, forced back on the thought of an ultimate unexplained power in virtue of which things have been created and are maintained in being.
The Lucretian hypothesis of the atoms, even if it were accepted as the most reasonable explanation of the original constitution of matter, is, by itself, altogether inadequate as a key to the secret of Nature. It cannot be shown either how these atoms succeeded in arranging themselves in order, or how from their negative properties all positive life has been produced. The explanation of physical phenomena given in the four last books, as to the nature of our bodies and souls,—as to the action of outward things on the senses,—the origin and existence of the sun and moon, the earth and the living beings upon it, etc., although professedly deduced from the principles established in the first two books, are really reached independently. They are either immediate inferences from the obvious intimations of sense, or they are the suggestions of analogy.
The weakness as well as the strength of ancient science lay in its perception of analogies. The mind of Lucretius was both under the influence of earlier analogical conceptions, and also shows great boldness and originality in the logical and poetical apprehension of 'those same footsteps of Nature, treading on diverse subjects or matters.' But, in common with the earlier enquirers of Greece, he trusts too implicitly to their guidance through all his daring adventure. He seems to believe that the hidden properties of things are as open to discovery through this 'lux sublustris' of the imagination, as through the 'lucida tela' of the reason.