of Pure Reason. However, from the content of the Dissertation, it is possible to argue that it might be regarded as a condition of the order of perception, a ‘schema’ in the sense of a pattern that provides unity and coordination and that space and time are linked to sensibility but do not derive from it.
Besides the above-mentioned occurrences of ‘schema’, there is another passage in the Dissertation which is of great interest for my inquiry:
“But pure (human) intuition is not a universal or logical concept under which, but a singular concept in which, all sensible things whatever are thought, and thus it contains the concepts of space and time. These concepts, since they determine nothing as to the quality of sensible things, are not objects of science, except in respect of quantity. These concepts, since they determine nothing as to the quality of sensible things, are not objects of science, except in respect of quantity. Hence, PURE MATHEMATICS deals with space in GEOMETRY, and time in pure MECHANICS. In addition to these concepts, there is a certain concept which in itself, indeed, belongs to the understanding but of which the actualisation’ in the concrete requires the auxiliary notions of time and space (by successively adding a number of things and setting them simultaneously side by side). This is the concept of number, which is the concept treated in ARITHMETIC.” (AA II, 397)59←50 | 51→
In these lines, Kant does not refer to schemata but to a number, which will be one of the particular, transcendental schemata exposed in the Critique of Pure Reason. This reference is important because it alludes to the way in which schematism will be developed: namely, the concepts of the understanding (such as number), can be actualised through time (and space).
After considering these references to the notion of schema, it is possible to synthesise its significance as the following: schema is no more a metaphysical concept (as it was presented in the Dilucidatio), but rather it obtains a more epistemic significance. It refers to the forms of sensibility, which are necessary conditions for providing the material elements of experience with organisation, thus explaining the possibility of experience and knowledge. This characterisation of space and time as schemata (or “quasi” schemata, as if Kant is using the noun schema without a proper definition) as conditions shares similarities, but also differences, with the doctrines of the Critique of Pure Reason: on the one hand, space and time are defined in the Transcendental Aesthetic as conditions of the possibility of the intuition, on the other, they become defined as pure intuitions and not as schemata (that will have a different function as illustrated in the Transcendental Logic). Nevertheless, there are passages in the Critique of Pure Reason in which they are still regarded as conditions (KrV A140/B179), although in a different sense as the forms of intuitions of space and time.
The value of the Dissertation might lie precisely in the doctrine of space and time and in their definitions as forms, schemata, which provide a solution to an important debate of the time, namely the conflict between empiricism and rationalism. However, Kant’s theory has its limits, which the author himself soon becomes aware of and which lead him to write the Critique of Pure Reason.
To underline both the novelties and the limits of Kant’s doctrine of space and time in the Dissertation and to understand why he will develop his theory of form and schema in the Critique of Pure Reason, it is helpful to refer to the main theories that he encountered concerning space and time, namely those of Isaac Newton and Gottfried Wilhelm Leibniz.←51 | 52→
In his famous treatise on light, Opticks (Newton 1730 (in part. Book III, question 31, pp. 350–382) Newton states that physics must abandon the study of qualities, which characterised the old Aristotelian view, focusing instead only on principles which can be empirically demonstrated. Principles must be distinct from obscure metaphysical causes (Newton 1730, p. 377): while the former are either immediately evident or proved by induction, the latter are often obscure or impenetrable, their relation to the events they are supposed to produce is unknown and lies beyond our possibility of knowledge. However, Newton seems to abandon the rigid separation between science and metaphysics when he refers to the existence of space and time as absolute in his Philosophiae naturalis principia matematica from 1687. This work led at first to the atheistic interpretation of Newton’s doctrine. Due to being accused of atheism, Newton was obliged to add a Scholium Generale to later publications of the work in order to defend himself.
The Scholium to the Definition of the Principles opens with the distinction between absolute and relative quantities, namely, of time and space. Time can be regarded as absolute, independent from the existence of things of experience but also as relative, as a measurement or limitation (hours, days, years) of the infinite duration of absolute time. In his attempt to provide an explanation of the existence of absolute space, Newton relies on the first law of motion: since the possibility of a rectilinear, uniform motion lies in the absence of acceleration, a reference to absolute time, which has no limitations and so can explain the possibility of such infinite movement, is needed. Together with absolute time, absolute space is presupposed, intended as the field in which bodies are situated: it is not a relation between objects, but rather a primary location, unique and with no relation to anything, but containing all relations within itself.
As presented, Newton alternates between the need to free science from metaphysical assumptions and the reference to principles whose nature cannot be scientifically justified. How can this ambiguity be explained? As Ernst Cassirer remarks, Kant will avoid the risk of mixing the sensible and intelligible realms (for instance, by referring predicates such as ‘where’ and ‘when’ to objects of the pure world, like God, and by grounding relative space and time on metaphysical principles): “The ‘infection’ the contagium, of the intelligible by the sensible, which emerges so clearly in Newton’s theory concerning God, is avoided;” ←52 | 53→(Cassirer 1922, p. 121, transl. L.S.)60. Maybe the clearest passage in which this problem can be seen is the following:
“He is not eternity or infinity, but eternal and infinite; he is not duration or space, but he endures and is present. He endures forever, and is everywhere present; and by existing always and everywhere, he constitutes duration and space. Since every particle of space is always, and every indivisible moment of duration is everywhere, certainly the Maker and Lord of all things cannot be never and nowhere.” (Newton 1687, transl. A. Motte, p. 441)61
In Newton’s work, on the one hand it seems that one of his main attempts consists in providing objective grounds to science through the reference to demonstrated claims, on the other hand these claims seem not to be sufficient, and need the reference to principles which belong to other fields of knowledge. Another and maybe easier solution is to stress the influence exerted on Newton by metaphysicians and theologians of the time, such as Henry More, and, in general, by his attempt to find a conciliation between science and religion so as to defend himself against the accusation of atheism.
Confronting the same question concerning the nature of space and time, Leibniz situated himself in direct opposition to Newton. His Epistolary with Samuel Clarke (between 1715 and 1716) can be regarded as emblematic of the contemporary focus on the relation between metaphysics and sciences and the nature of the principles of knowledge. The epistolary originates from a letter sent by Leibniz to Caroline of Wales, in which he distanced himself from the Newtonian theory of absolute space and time. Then she put the philosopher in contact with Clarke, a theologian of Westminster and defender of Newton’s perspective. Influenced by the recent publication of the paradoxes of Zenon in Pierre Bayle’s Dictionnaire historique et critique (Bayle 1702) Leibniz affirms that space cannot be absolute, otherwise there would be something that cannot be explained by a cause, as required by the principle of sufficient reason: if space were uniform,
