Hobbes, Thomas (1588–1679)

3. The elements of philosophy: logic and metaphysics

The relative positions of the two parts of science – natural and civil – are reflected in the organization of Hobbes’ trilogy on the elements of philosophy. The first volume, De corpore, expounds first philosophy, geometry, mechanics and physics. It is followed by De homine, which is half optics and half psychology; this volume in turn is supposed to prepare the ground for the exposition of the elements of ethics and politics in De cive.

The account of the ‘elements’ of science starts in De corpore with chapters on the ways in which philosophy depends on names, propositions and methods of reasoning. For Hobbes, logic is nothing more than the right ordering and joining of significant propositions into chains of reasoning. Propositions in turn are no more than coherent concatenations of names with significations of different extents. A name signifies an idea – whatever idea it conveys in the context of a speech to a hearer. But the idea is not what the name refers to or stands for: it refers to or stands for an object. To make a proposition, names have to be put together coherently, and coherent concatenations are concatenations of the same category of name – names of bodies with names of bodies, names of names with names of names. The ‘extent’ of the signification of a name has a bearing on the truth of propositions. The signification of a proper name will extend to an individual, that of a universal name – ‘man’, ‘horse’, ‘tree’ – to each of a plurality of individuals. In the propositions of natural science, names are universal names of bodies. Truth in the propositions of natural sciences is a matter of the inclusion of the extent of a universal subject-term within the extent of a universal predicate-term. Demonstrations are chains of syllogisms, and syllogisms are the stringing together of trios of propositions that share appropriate subjects and predicates. In a sense, then, logic is a technique for working out the consequences of relations between the significations of universal names or their extents. There are also methods belonging to logic for analysing the significations of names, and for arriving at the most general of these significations from a starting point in everyday universal names. Logical analysis of this kind is what is required to locate the terms fundamental to the various branches of science; it also has a role in making scientific questions amenable to resolution. Metaphysics or first philosophy sets out, ideally by means of definitions, the concepts necessary for conducting fruitful enquiries concerning natural bodies and for communicating the results. The relevant concepts include those of body, motion, time, place, cause and effect.

Hobbes composed no full-scale treatise on logic, and no work of his is concerned with metaphysics alone. De corpore contains the nearest approximation to a full first philosophy, and even here he is not entirely clear about the borderline between that ‘prior’ science and geometry. There is a chapter on ‘syllogism’, but it is not comprehensive and its relation to traditional syllogistic is never spelled out. As for the chapters on first philosophy, they are more significant for what they deny than for what they affirm. They deny that it makes sense to study ‘being’ in the abstract; they deny that species or genera are things; they deny that ‘substance’ can mean something very different from ‘body’; and they deny that other predicables are more than varieties of sensory appearance caused by bodies. In short, they deny much standard Aristotelian doctrine, including the doctrine defining the subject matter of metaphysics itself – the doctrine that metaphysics studies being qua being. As will become clear, the chapters on first philosophy can also be understood to register disagreements between Hobbes and some of the moderns –Descartes and Gassendi, among others.

Hobbes’ first philosophy starts with a thought experiment. He imagines that the external world has been annihilated – all that remains is a single thinker and the traces in memory of the world he previously sensed and perceived. Hobbes claims that the disappearance of the external world would not take away conditions for thought or reasoning, even about the physical world. The annihilation of the world would not even alter conditions for such thought and reasoning, since the medium of thought and reasoning is never things themselves but only appearances or phantasms. Hobbes thinks that the annihilation of the external world leaves only the mind and its phantasms in existence. There is no third world of things that exist outside the mind but outside the physical world as well. So Hobbes denies that there exist without the mind abstract natures such as Descartes claims to discover in Meditation V; and, contrary to Gassendi in the Syntagma, he does not think that space and time are real independently of the mind. He derives the idea of space from the memory images or phantasms presenting things as if from outside the mind. He derives the idea of time from imagined motion, from succession without existence. He derives the idea of an existing thing from the imagination of an empty space suddenly getting an occupant. Existence is thus restricted to existence in space, which is in turn identified with corporeal existence. These resources allow for only a straitened conception of cause or power, and certainly not for an Aristotelian conception. There are no forms or purposes in nature; but the makings of a conception of efficient cause are available, and that is the only sense of ‘cause’ recognized by Hobbes’ first philosophy.

Most of the concepts that Hobbes thinks are needed for natural science have now been indicated. In Part Two of De corpore, after defining ‘time’ and ‘place’, he thinks he is in a position to define ‘body’ and its most general accidents. He then deals with magnitude or real space-occupation, and the spatial relations of continuity and contiguity. Against this background he defines ‘motion’, and in terms of motion the ideas of length, depth and breadth. After the three spatial dimensions are explicated, he defines quantitative identity and difference for motions and bodies, and then discusses the conditions of qualitative difference between bodies over time. He goes on to consider the causes of qualitative change, concluding with a demonstration of the thesis that all change is motion, that motion is the only cause of motion, and that power (potentia) is nothing but motion in so far as it is a cause of motion.

Definitions dominate Hobbes’ first philosophy and, officially at least, their purpose is to fix ideas necessary for the business of science proper. Hobbes thought that the mark of a prescientific branch of learning was controversy, and he traced controversy to a failure to define terms and to proceed in orderly fashion from definitions to conclusions. The task of first philosophy is to provide insurance against controversy. It does not do this by coming up with substantive truths that command assent. Instead, Hobbes describes first philosophy as a necessary preliminary to the demonstration of substantive truths, where demonstrator and learner are put on one another’s wavelength and attach the same significations to their terms, but where their agreement is terminological rather than doctrinal. As Hobbes puts it in the Six Lessons, ‘he that telleth you in what sense you are to take the appellations of those things which he nameth in his discourse, teacheth you but his language, that afterwards he may teach you his art. But teaching of language is not mathematic, nor logic, nor physic’ ([1656b] 1839 VII: 225).

That ‘the teaching of language’ underdescribes what Hobbes does in practice in stating his first philosophy, and that it suppresses entirely the revisionary character of some of his definitions when compared with Aristotelian ones (and so the controversial nature of the devices that are supposed to pre-empt controversy), should already be clear. But, up to a point, Hobbes’ first philosophy is genuinely unassuming. It takes for granted no exotic powers or substances, God included, and it postulates no exotic human capacities for acquiring the concepts that are the key to natural science. The point is not just that Hobbes keeps the relevant concepts to a small number, so that he is economical in the concepts he uses and also in his assumptions about the types of real things there have to be for these concepts to be applicable. Hobbes’ first philosophy is also naturalistic. Nothing supernatural is assumed to exist in order for natural science to be acquired; indeed, nothing besides matter in motion is postulated. What remains after the annihilation of the world in Hobbes’ thought experiment is not the immaterial self of Descartes, but the corporeal body or perhaps the brain, and the motions conserved in its internal parts from past impacts of the external world on the sense-organs.

The denial of immaterialism in Hobbes’ first philosophy is anticipated in his Objections to Descartes’ Meditations. An objection that Hobbes directs at Meditation II sets the tone (see Descartes, R. §5). He accepts that from the fact that I am thinking it follows that I exist, but he wonders whether Descartes can properly conclude, as a corollary, that the I is a mind or an intelligence or a thinking thing. For all the Cogito shows, Hobbes says, the I could be corporeal. And not only does the Cogito leave open the possibility of the I being corporeal, he goes on, the later wax argument actually shows that the I is corporeal:

Descartes’ reply concedes that acts need subjects, that it is a thing that is hard, changes shape and so on, and also a thing that thinks, but he insists that ‘thing’ in this sense is neutral between the corporeal and the spiritual. He insists, too, that he is non-committal about the nature of the thing that thinks in Meditation II, a claim borne out by his responding agnostically in Meditation II to the question of whether he might be a structure of limbs or a thin vapour. If Hobbes misses that, it may be because he misunderstands the rules of the method of doubt. While implementing the method of doubt, Descartes does assume rather than prove that there is no body for the thinking thing to be or for the thought to inhere in. But this is not a case of begging the question, for the belief in the existence of bodies is reinstated in Meditation VI, and with that the question of whether the subject is essentially immaterial or material.

Hobbes comes at Descartes’ immaterialism from another, more revealing direction when he tries to suggest that it is not needed to underpin the distinction between imagination and conception by the mind. In his fourth objection, Hobbes equates imagination in Descartes’ sense with having an idea of a thing, and conception in Descartes’ sense with reasoning to the conclusion that something exists. Descartes already agrees that imagination is a partly corporeal process resulting from action on the sense organs, but his text suggests that conception by the mind is an altogether different operation. Hobbes puts forward a suggestion that allows the explanation of conception and imagination to be linked, without the postulation of immaterial things. He proposes that reasoning is the process in which labels attached to various things are concatenated into sentences according to conventions agreed by humans.

The compatibility of this proposal with mechanistic explanation appeals to Hobbes; but Descartes raises some powerful doubts about Hobbes’ idea that names alone come into reasoning. Contrary to Hobbes, Descartes takes it that reasoning is a matter of linking together the significations of names, not just the names themselves, and also that the significations of some names cannot be imaged.

As in the case of his objection concerning the subject of the thinking, which seems to overlook the constraints of the method of doubt, Hobbes’ objection to Descartes on imagination and conception seems to miss the point. Descartes is not trying to explain the workings of the faculties that result in science, only to find that he has to explain them on immaterialistic principles. He is trying to show that science is possible, that real knowledge of the physical world is possible, because not all of our faculties can coherently be held to be unreliable. Conception by the mind is a case in point. It cannot be held to be unreliable, because it is autonomous and independent of unreliable sense-perception. Hobbes does not see that it is the objectivity of conception rather than the process of conception that Descartes is concerned with. And doubting the objectivity of conception himself, Hobbes does not seek to reconstruct conception as reasoning that might be guaranteed to lead to true conclusions; he wants only to reconstruct it in ways that will not multiply entities beyond those required by mechanistic explanation. The point is that a proof of the objectivity of the conceptions arrived at by science may legitimately be demanded of a metaphysics, and Hobbes’ metaphysics does little if anything to meet the demand. The metaphysical economy of materialism will not impress someone who is sceptical of the existence of the external world: the undeniability of the Cogito might. One cost of Hobbes’ naturalistic approach is that it never attempts the task of legitimizing the scientific enterprise in general, and is probably incapable of doing so.