The modality of force

To properly account for the role of touch, we need to take another look at the modality of matter on Kant’s account. Kant’s discussion of modality is shaped by his essentialism about matter.60 He writes:

A property on which the inner possibility of a thing rests, as a condition, is an essential element thereof. Hence repulsive force belongs to the essence of matter just as much as attractive force, and neither can be separated from the other in the concept of matter. (MAN 4: 511)

The real essence of matter is the ground that explains all its other properties. This contrasts with the logical essence of matter, which is whatever is contained in the

60 _{Several different readings lead to a similar account of matter. See Stang (2016) on Kant’s}

essentialism about matter, Watkins (2004) on Kant’s causal power model of causation, and Langton (2001, pp. 175–178, 2018; Langton & Robichaud, 2010) on Kant’s account of phenomenal substance.

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concept of matter, as the ground of everything else contained in that concept (see Stang, 2016, p. 234). Repulsive and attractive forces are needed to make matter what it is – without them, matter could not fill space. Thus, forces are part of the real essence of matter.

Kant attributes a necessary aspect to force: matter has a real essence, constituted by forces, which grounds the necessity of the properties of matter. Given the real essence of matter, any part of matter behaves in certain ways when brought into relation to other parts, attracting and repelling them (MAN 4: 497f.). The real essence of matter grounds the laws governing the causal interaction between parts of matter. Thus, Kant holds a causal power model of causation, according to which a cause is the power of a part of matter to act in accordance with its real essence to determine effects. The necessary aspect is not all there is to the modality of force. Kant links the concepts of substance and matter, revealing a contingent aspect of force. As this link has been explored in depth by previous commentators, I mention only the points relevant to Kant’s ascription of contingency to force (see Guyer, 1987, pp. 232–233; Langton, 2001).

Kant claims that matter plays the role of phenomenal substance through its real essence, filling and persisting in space through forces. In discussing phenomenal substance, Kant has already moved beyond the pure concept of substance as ‘a something that can be thought as a subject (without being a predicate of something else)’ (A147/B186). The pure concept of substance is limited: ‘Now out of this representation I can make nothing, as it shows me nothing at all about what determinations the thing that is to count as such a first subject is to have’ (A147/B186f). The pure concept does not apply in experience, let alone determine the properties that substance has in space. Thus, Kant offers a schematized concept of substance, which tells us to look for a substratum for the time-determination of objects (A144/B183). This adds some spatio-temporal content – substance is that which endures through changes in other objects. But the schematized concept still only tells us about the effects brought about by substance, namely its endurance in space. It does not involve the real ground of matter, so it does not show how substance endures in space. The beginnings of an answer are only provided when Kant equates matter with phenomenal substance:

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Matter is substantia phaenomenon. What pertains to it internally I seek in all parts of space that it occupies and in all effects that it carries out, and which can certainly always be only appearances of outer sense. I therefore have nothing absolutely but only comparatively internal, which itself in turn consists of outer relations. (A277/B333)

As Langton explains, absolutely intrinsic properties of a thing involve ‘no relation whatsoever […] to anything different from itself’ (2001, p. 34). Such properties include the solidity and geometrical extension of a substance, which are specified only in terms of that substance. These properties do not determine how, if at all, the substance relates to other things. In particular, they underdetermine whether substance fills space by interacting with other substances. By contrast, force is a relational property of a part of matter, defined entirely by its action (attraction or repulsion) on other parts of matter. The real essence of matter, as constituted by forces, is comparatively intrinsic, ‘in the sense that it explains the manifest character of matter and in the sense that it is essential to matter’ (Stang, 2018, p. 484).

The forces of matter are the comparatively internal – that is, relational – properties of substance. This link between matter and substance allows Kant to ascribe a contingent aspect to force. To use possible-world terminology, there are possible worlds where substance has the same absolutely intrinsic property of occupying space – solidity or geometrical extension – but different relational properties, which ground different laws of nature. In these worlds, substance is not constituted by forces. To use Langton’s example, in some such worlds, one could walk through walls which occupy space, but do not fill space by the forces of matter.

Therefore, Kant has a more complex modality of matter than suggested by Marshall’s Puzzle. Marshall offers the following modal picture: there are singular events or states of affairs in sequence, with causal, hence necessary, relations holding between them. The Puzzle arises from our inability to perceive these necessary relations. But Kant has a different modal account: there are parts of matter, with a real essence grounding the relations between them. Forces are the real essence of matter, grounding the necessity of its properties. It is contingent that forces play the role of substance – something with a different real essence could have played the role, so parts of matter could have interacted in very different ways, or not at all.

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