 Kant also uses the term ‘spontaneity’ in a somewhat different sense in a metaphysical context, to refer to a mental cause that can sufficiently determine an effect in time while also lacking any temporally prior sufficient cause of itself (A445/B473). Call this practical spontaneity. What is shared between the two senses of spontaneity, practical and cognitive, is the unprecedented, creative character of the mind’s operations. But in the cognitive sense of spontaneity, what is crucial is that the sensory data manifest “poverty of the stimulus” (Cook &amp; Newson 1996, 81–85)—significant underdetermination of the outputs of an embodied cognitive capacity by the relevant inputs to that capacity, plus previous experiences or habituation—although the faculty’s spontaneity must also always be minimally conditioned by external sensory triggering (B1–2). Correspondingly, a Kantian cognitive faculty is innate in the threefold sense that (i) it is intrinsic to the mind, hence a necessary part of the nature of the rational animal possessing that faculty, (ii) it contains internal structures that are necessarily or strictly underdetermined by any and all sensory impressions and/or empirical facts—which is the same as their being a priori (B2), and (iii) it automatically systematically synthesizes those sensory inputs according to special normative rules that directly reflect the internal structures of the faculty, thereby generating its correlatively-structured outputs. So Kantian innateness is essentially a procedure-based innateness, consisting in an a priori active readiness of the mind for implementing normative rules of synthesis, as opposed to the content-based innateness of Cartesian and Leibnizian innate ideas, according to which an infinitely large supply of complete (e.g., mathematical) beliefs, propositions, or concepts themselves are either occurrently or dispositionally intrinsic to the mind. But as Locke pointed out, this implausibly overloads the human mind’s limited storage capacities.