Aristotle’s talk about ends was part of a pragmatic semantics of experience, in which so-called efficient causes were understood mainly as means. In the later tradition, however, talk about ends, or teleology, acquired a strongly theological coloring, and events in time were often conceived as directly governed by divine will. Then early modern mechanism strove to give an independent account of nature in mathematical terms. Twentieth-century mathematics developed notions of attractors, which at least function in a way broadly like ends rather than impulses, but early modern mechanists wanted to explain nature without any recourse to teleology. The debate was posed in terms of mathematics versus invocations of divine will.
Kant struggled with these early modern dilemmas, seemingly unaware of the historical Aristotelian way of looking at the matter. Like the Critique of Practical Reason, the Critique of Judgment was aimed at reconciling Newtonian mechanism with broadly theological values. In the second Critique, he said that while we cannot have theoretical knowledge of freedom, it is a necessary practical postulate. In the third, which was initially about aesthetic judgment, he concluded that although we have no theoretical basis for affirming actual purpose in nature, thinking about purposes is nonetheless a practically useful heuristic, particularly in the case of biology. Kant ultimately argued for the primacy of practical reason, so this “merely” practical perspective is actually fundamental. (See also Natural Ends.)