his Dedication of De corpore to the Earl of Devonshire, Hobbes employs another analogy to make a similar point about Scholastic Aristotelian philosophy, characterizing it as the Empusa of the Athenian comic poet: “there entered a thing called school divinity, walking on one foot firmly, which is Holy Scripture, but halted on the other rotten foot, which the Apostle Paul called vain, and might have called pernicious philosophy” (EW I.xi). Hobbes proposes to exorcise this monster by distinguishing
between the rules of religion, that is, the rules of honoring God, which we have from the laws, and the rules of philosophy, that is, the opinions of private men; and to yield what is due to religion to the Holy Scripture, and what is due to philosophy to natural reason. And this I shall do, if I but handle the Elements of Philosophy truly and clearly, as I endeavor to do.
(EW I.x–xi)
He then announces the aim of this work:
I intend now, by putting into a clear method the true foundations of natural philosophy, to fright and drive away this metaphysical Empusa; not by skirmish, but by letting in the light upon her.
(EW I.xi)
To build a political structure that will prove stable and lasting, one first requires true foundations of natural philosophy. These are to be treated methodically, unadulterated by the mixing in of myths, fables, and religious writings. From the start, Hobbes presents his new moral and civil science as dependent on the true foundations his method provides for natural philosophy. Method is crucial to Hobbes’s project.
Hobbes’s purging of the non-natural from philosophy in order to base practical philosophy on the scientific foundations of natural philosophy does not imply that he rejects all religion and theology – note that the rotten foot is the philosophical one! Rather his colorful analogies trace the lack of progress in practical philosophy to the intermingling of philosophy and religion. A methodical treatment of the true foundations of natural philosophy required for a moral science thus necessitates that one first cordon off the domain of philosophical activity, which De corpore’s Epistle to the Reader describes as “the natural reason of man, busily flying up and down among the creatures, and bringing back a true report of their order, causes and effects” (EW I.xiii). Fencing in natural reason prevents it from encroaching on and contaminating neighboring territories. The goal is not to obliterate religion, but to confine philosophy to what Hobbes regards as its proper domain, and thus to contain and purify both. He even suggests that philosophy (which, like René Descartes, he takes to reside confusedly within us) requires a method that keeps the contemplative order separate but parallel to the order of creation.1
Hobbes’s characterizations of his project, reveal that his formal definition is designed to put Philosophy, and its practitioners, in their place. Philosophy is,
such knowledge of effects or appearances, as we acquire by true ratiocination from the knowledge we have first of their causes or generation: And again of such causes and generations as may be from knowing their first effects.
(EW I.2)
As Hobbes acknowledges afterward, this is a narrower definition than was typical of contemporaneous philosophers. It also equates natural reasoning with ratiocination, which Hobbes characterizes narrowly as computation, a mental composition and resolution of conceptual units which I discuss in the final section. Armed with his definition Hobbes deduces from it that the subject of philosophy is delimited to,
every body of which we can conceive any generation, and which we may, by any consideration thereof, compare with other bodies, or which is capable of composition and resolution; that is to say, every body of whose generation or properties we can have any knowledge.
(EW I.10)
Philosophy, and its activity of ratiocination, is thus confined to the domain of material things. Angels, being immaterial, are excluded, as is Theology, since God is unchanging and eternal. The narrowing of natural reasoning to computation also excludes subjects that rely on other forms of knowing from the domain of Philosophy. Hobbes thus rules history, revealed knowledge, doubtful doctrines like astrology, as well as the doctrine of God’s worship out of bounds (EW I.10–11).
In sum, Hobbes places two constraints on philosophers that shape their method. First, he limits them to reasoning, which, equated with computation, brings in the second constraint. Such computation applies only to body, of which there are only two kinds: natural bodies, which are works of nature and the subject of natural philosophy, and the Commonwealth, an artificial body, made by the wills and agreement of humans, which is the subject of civil philosophy. To understand Hobbes’s method for attaining a civil science that rests on true foundations, one must recognize that his natural philosophy encompasses both less and more than Scholastic natural philosophy and absorbs what we call STEM today. Chapter IX of the English edition of the Leviathan divides natural philosophy into knowledge of the consequences of the common accidents of bodies, and of the consequences of their qualities. The former is subdivided into First Philosophy, Geometry, Arithmetic, Astronomy, Geography, Engineering, Architecture, and Navigation. The consequences of bodily qualities are studied by Physics, which is further subdivided into Sciography, Meteorology, Optics, Music, and Logic.2 Unlike De corpore, the Leviathan places Ethics, and Astrology, Poetry, Rhetoric (all three of which De corpore excludes from Philosophy) plus what Hobbes calls “the science of the just and unjust” under Physics (2012, 130–1; 1651, 40–1). The Leviathan limits civil philosophy to knowledge of the consequences of “politic bodies” (2012, 130–1; 1651, 40–1) whereas De corpore further subdivides it into ethics, which treats of human dispositions and manners, and politics, “which takes cognizance of their civil duties” (EW I.11).
Regardless of which classification one follows, for Hobbes, natural philosophy consists in 1) knowledge of first principles, i.e., foundational definitions that provide the starting points for scientific demonstration (First Philosophy), 2) pure and applied mathematics, and 3) a varying collection of crafts useful to human life. Most Scholastics placed First Philosophy under metaphysics, and the rest either under pure and mixed mathematical sciences or under the arts.3 Civil philosophy, for Hobbes, primarily concerns the commonwealth and the duties plus rights of its subjects. Ethics straddles natural and civil philosophy; insofar as it studies human manners and dispositions as qualities of human bodies it belongs to physics, insofar as it draws from them the rights and duties of subjects, it belongs to the new civil science. Contrary to our natural/normative divide, Hobbes places theoretical and practical philosophy on a continuum, with ethics in mid-range. Scholastic metaphysics, as the science of being qua being, and parts of Aristotelian natural philosophy that challenge theology, like the study of the first cause of motion, biology, and the soul (qua principle of life) have been purged.4
With the Empusa exorcised, philosophy confined to the study of body and traditional metaphysics firmly under religious control, Hobbes then broadens natural philosophy to include mathematical sciences. Thus the reach of philosophical ratiocination is extended to crafts, like mechanics and engineering, that renaissance philosophers had elevated to scientiae.5 Like his contemporaries, Hobbes defines scientia as knowledge consisting in deductive proofs known as syllogisms. In the ideal type of scientific syllogism, which takes the form of propter quid demonstrations discussed in Aristotle’s Posterior Analytics, one reasons deductively from a premise that identifies the cause or explanatory factor (typically a definition), to its effect or consequence. Aristotle developed rules for constructing logically valid syllogisms, which the beginning of De corpore like most contemporaneous textbooks, covers summarily. Hobbes follows textbooks that combine Aristotelian and Ramist logic, adding a chapter on Method to his Logic. There he makes the standard claim that the deduction of causes through valid syllogistic reasoning is what scientific knowledge aims at:
The end of science [scientia] is the demonstration of the causes and generations of things; which if they be not in the definitions, they cannot be found in the conclusion of the first syllogism, that is made from those definitions; and if they be not in the first conclusion, they will not be found in any further