In a chapter on “The Ground of the Distinction of All Objects in General into Phenomena and Noumena,” Kant writes, “Everything which the understanding derives from itself is, though not borrowed from experience, at the disposal of the understanding solely for use in experience” (Critique of Pure Reason, in Modern European Philosophers, 409). Each of them is a “pure schema of possible experience” (409).
Why so? Well, Kant reasons, “The understanding can employ its various principles and its various concepts solely in an empirical and never in a transcendental manner…The transcendental employment of a concept in any principle is its application to things in general and of themselves; the empirical employment is its application merely to appearances; that is, to objects of a possible experience” (410). Only the latter is possible, because the application of a concept requires a) grasping its “logical form,” and b) “the possibility of giving it an object to which it may apply” (410). He goes on to insist, “The most the understanding can achieve a priori is to anticipate the form of a possible experience in general” (411). The understanding’s “principles are merely rules for the exposition of appearances” (411). The horizon of experience thus becomes an iron cage constraining human thought.
Consider Kant’s application of this rule to the particular case of “causality.” A few pages prior, he insists that, while “the stove, as cause, is simultaneous with its effect, the heat of the room” (so siding with the scholastics against Hume), and while “the time between the causality of the cause and its immediate effect may be a vanishing quantity, and they may thus be simultaneous; but the relation of the one to the other will always still remain determinable in time” (408). Causality is intrinsically a temporal category, and so “if I omit from the concept of cause the time in which something follows upon something else in conformity with a rule, I should find in the pure category nothing further than that there is something from which we can conclude to the existence of something else. In that case not only would we be unable to distinguish cause and effect from one another, but since the power to draw such inferences requires conditions of which I know nothing, the concept would yield no indication how it applies to any object” (410-11).
Kant’s point is simple: the concept “cause” is so pervasively conditioned by reference to time that “a-temporal” causation is simply meaningless; causality is a name for the ordered and rationally-explicable sequence of events in time. He hasn’t yet applied this analysis to the so-called “cosmological argument” from the world to the LORD as its cause, but the application is clear — such an analogical ascription of causality to the LORD qualifies it to the point of meaninglessness.
But now note the dialectics that ensue when he attempts to explicate the intrinsic connection between causality and time: he recognizes that Hume was wrong to see cause and effect as two contiguous events; it’s much better to say that cause and effect are one event, viewed under the aspects of agency and passivity, respectively. But in that case, it’s not obvious that the idea of temporal sequence has any necessary connection with the notion of causality — rather, the fundamental order seems to be that of logical priority (if not A, then not B), with temporal order filling a subordinate, explanatory role in some cases (i.e., John is the father of James who is the father of Jack, and so John is a cause (per accidens) of Jack).
Indeed, Kant’s attempts to so qualify temporal succession as to include absolutely simultaneous events (i.e., a “vanishing quantity” of time) strikes me as much closer to the sort of conceptual death-by-a-thousand-qualifications that he warns against than anything you’ll find in Aquinas.