§47. Against Empiricism
“Hobbes is simply an Aristotelian malgre lui” a scholar of his natural philosophy concludes. His theory of knowledge is an empiricism on the model of Aristotle, and is more Aristotelian than empirical in a modern sense, especially in his idea of science, which is not empirical in the least.
“I do not here examine things by sense and experience,” he sniffs, “but by reason.”187He divides knowledge into two kinds: knowledge of fact, which is the work of sense and memory; and knowledge of consequences, logical knowledge of what follows from what. The senses and memory are forms of knowledge (cognitiones), but not of such knowledge as can be derived rationally from principles, hence not science, that is, Aristotelian demonstrative scientia. Epitomizing Aristotle, he describes experience as “much memory,” and what we remember are perceptions. Experience promotes prudence, but by itself cannot advance natural philosophy. The first step toward science is to codify experience with names, artificial marks to designate what we have many times met with in perception. Combined in logical complexes that are true or false, these propositions can be further combined into syllogisms, and therewith science starts.
Knowledge is either empirical and practical, comprising perceptions, memories, and conjectures, or it is scientific knowledge of causes. To understand the cause of a thing scientifically is to understand the principle from which it is deduced. Hobbes explains the “entire cause” of an effect as “the aggregate of all the accidents... which when they are all supposed to be present, it cannot be understood but that the effect is produced at the same instant,” an explanation that began with the Hippocratics and was perfected by the Stoics. For such causes experience cannot be a source of knowledge. Geometry does not wait for experience to know of points generating lines, and natural philosophy does not wait on experience to deduce the motions of nature. Motion is for Hobbes a purely geometrical idea.
The mechanical possibility of a motion is its geometrical possibility. The object of physics is to find the causes of sense appearances—possible causes, geometrically demonstrated. He is interested only in saving the phenomena.188“It is deduction on which Hobbes's interest is focused,” the same scholar writes. “As soon as he has seen a possible cause, that is to say, as soon as he has demonstrated that from this cause the effect may be understood, he is satisfied. Further verification he does not seek.” For example, in a discussion of the solar system Hobbes writes, “Though the causes I have here supposed be not true causes of these phenomena, yet I have demonstrated that they are sufficient to produce them.” The proof of that sufficiency, a mechanism that could produce the effect, is all he expects of scientia. He generalizes Epicurus's thesis on the physics of celestial phenomena (§17), allowing multiple causes, and (also like Epicurus) is uninterested in trying to prove the true conditions of the effect. The most that can be expected in natural philosophy is that mechanical generation be conceivable and consistent, with nothing contrary to the phenomena deriving from their hypothetical existence.189
Galileo never lost sight of experience, and his mathematics always returns to experiment for verification. “Thus it must be in these domains of knowledge in which mathematical proofs are applied to natural consequences.” Boyle took this to heart. “What we are to inquire after, is, how things have been, or are really produced.” Without experiments the matter does not interest them. Though Hobbes claimed to esteem none above Galileo, his emulation is selective, admiring the mechanics and ignoring the experiments, proceeding blithely in his deductions without any of Galileo's “anxious looking backwards and forwards to sense-experience.”190