bodies generated by motions) whose passions and desire for peace make a social contract necessary. Two mechanical analogies suggest that Hobbes employs demonstration in this sense to methodically arrive at civil science. But since only artificial bodies of geometry and politics can be thus constructed this would imply that either physics lies outside of science, or Hobbes has distinct methods for theoretical and practical science.13 I argue, instead, that Hobbes has one method, but not a constructive method in this sense.
Hobbes’s use of mechanical analogies give the impression that civil science employs a method of mechanical construction at odds with method in physics. In De cive, Hobbes claims to have started from the matter of civil government “and thence proceeded to its generation and form, and the first beginning of justice. For everything is best understood by its constitutive causes” (EW II.xiv). Immediately thereafter he makes an analogy to a watch, which one must take apart to understand the matter, shape, and motion of the wheels. Similarly,
so to make a more curious search into the rights of states and duties of subjects, it is necessary, I say, not to take them insunder, but yet that they be so considered as if they were dissolved; that is, that we rightly understand what the quality of human nature is, in what matters it is, in what not, fit to make up a civil government, and how men must be agreed amongst themselves that intend to grow up into a well-grounded state.
(EW II.xiv)
In Leviathan, the Commonwealth or State is likened to an artificial person, which one can dissect into its component parts by analogy to the parts of an automaton. This analogy likewise suggests a kind of reverse-engineering methodology not possible with natural phenomena. Here too Hobbes employs Aristotelian notions of a form that is generated, and the matter, or constitutive causes, which once extracted through resolution, can then be recomposed in the correct way. A common interpretation equates Hobbes’s reference to resolution in this passage with his method of analysis in De corpore and aligns the re-composition with synthesis. Next I show that analysis and synthesis in De corpore are not a material resolution and re-composition. Here I argue that these analogies are rhetorical.
The automaton analogy precedes Hobbes’s description of the structure of his work, the Leviathan. He frames it in terms of the four causes familiar to his Aristotelian-schooled readers. First he treats of human beings, the matter, i.e., material cause, of this artificial body. Next, Hobbes invokes how the commonwealth is made by covenants, which to his readers would evoke its efficient cause. The last two sections of the book explain what a Christian commonwealth is and what the kingdom of darkness is, i.e., the final and formal causes (2012, 18; 1651, 2). Hobbes’s automaton analogy is a rhetorical visualization for the organic structure of his work, informing readers that he will present his theory starting from material and efficient causes and concluding with final and formal causes of the Commonwealth. Just as he does not thereby commit himself to a method that employs Aristotelian causes, his mechanical analogies do not commit him to a method of geometrical construction. Indeed, Hobbes’s De corpore clarifies that knowing scientifically is to syllogize from cause to effect.
The section that follows Hobbes’s etymological tracing of “demonstration” back to the ancient Greek geometrical term reveals a different sense of “demonstration”:
It is proper to methodical demonstration, First, that there be a true succession of one reason to another, according to the rules of syllogizing delivered above.
Secondly, that the premises of all syllogisms be demonstrated from the first definitions.
(EW I.87)
The formal definition of “demonstration” Hobbes gives just before he invokes its ancient origins confirms that it is “a syllogism, or series of syllogisms, derived and continued, from the definitions of names, to the last conclusion” (EW I.86). Hobbes’s recounting of the ancient geometrical sense of “demonstration” is thus a historical side bar to motivate putting geometry at the foundation of scientific knowledge by appeal to the ancients. Once geometry makes visible its foundational definitions, scientific reasoning proceeds syllogistically.
The rhetorical purposes of the watch and automaton analogies, combined with Hobbes’s formal definitions of scientific knowledge and “demonstration” caution against taking mechanistic resolution and re-composition as Hobbes’s method for civil science.14 Nonetheless, De corpore’s analogy between all definitions and geometrical ones reinforces the impression that Hobbes’s method of demonstration is one of construction:
But definitions of things, which may be understood to have some cause, must consist of such names as express the cause or manner of their generation, as when we define a circle to be a figure made by the circumduction of a straight line in a plane, & c.
(EW I.81–2)
But Hobbes also affirms the Scholastic view that principles are indemonstrable, adding that there are no principles aside from definitions (EW I.80, 82). Properly speaking, definitions are not demonstrated; hence their generation is not scientific ratiocination or computation. So, though one might make visible the definitions of natural and civil philosophy in a way that parallels geometrical construction of a figure, this is only a demonstration in a loose, analogous sense. Hobbes’s analogies thus do not support the bifurcation into a demonstrative method of construction in civil science versus the physicist’s method.
With this confusion removed, can we now articulate a unified method that would legitimize Hobbes’s claim to inaugurate a moral science based on the true foundations of natural philosophy? Even having restricted scientific knowledge derived from the primary geometrical definitions to Hobbes’s narrow sense of propter quid demonstrations, this remains challenging. If the success of Hobbes’s project rests on the capacity of his method to provide a true foundation of definitions or principles about universal causes from which, through a unified chain of syllogisms, ever more specific and complex effects are deduced, then it seems to fail. Notwithstanding that all scientific knowledge is knowledge of bodies, there are key differences between the aspects of body that each individual science takes as its object.
Natural philosophy scientifically knows what follows from the accidents of natural bodies whereas civil philosophy scientifically knows what follows from the accidents of the artificial body that is the commonwealth. Within natural philosophy, geometry, which lies at the base of the hierarchy in De corpore, takes as its object the accidents common to all bodies whereas physics takes as its object qualities, i.e., accidents of bodies as sensed by humans. This implies that the application of Hobbes’s generic method varies with object. As scholars have long realized, Hobbes’s actual procedure in physics differs from that of geometry and civil science since we are not privy to the underlying causes of the bodily qualities we sense.15 In physics one cannot define a quality by mentally constructing it, as one does with the generative definition of a square or when one imagines a commonwealth coming into being. Rather one must begin from observed effects, like the reddish hue of the setting sun or the passion of joy we feel when we watch it, and reason hypothetically to their possible causes. Since physics lies in the middle of the hierarchy of scientific knowledge providing the bridge between geometry and practical philosophy, if one assumes that unity means the sciences present a unified content, via an axiomatic-deductive method whereby all their conclusions trace back through a seamless chain of deduction to the same foundational definitions, then the divergent methodical procedure necessitated by the objects of physics appears to disrupt the unity of the whole.
In the face of these problems, one can 1) deny that Hobbes maintains a unity of theoretical and practical philosophy or 2) affirm a looser unity by denying that it is conditioned upon an axiomatic-deductive method. Advocates of 2) present evidence of Hobbes’s commitment to a non-deductivist unity. I draw on two recent views of this unity to propose a third. 2a) reads Hobbes’s sciences as unified not by a systematic content ultimately deduced from first principles, but by a common “demonstrative” method analogous to the geometrical method of construction.16 This strikes me as the correct strategy; however, though one finds procedures resembling constructions throughout Hobbes’s works, they cannot, as