In the Critique of Pure Reason, Kant establishes sensation and concepts as the two ultimate foundations of cognition, which, while possibly having a common root, are (as regards the structure and prerequisites of cognition) to be clearly distinguished. According to Kant, the differences between the two foundations of cognition are both real and methodological. Sensation is passive, and depends on stimuli from without, while thinking or conceptualization is active, spontaneous and self-moving. Thus the factual difference between the two 'stocks' of cognition consists in the passivity of the one and the activity of the other. The methodological difference between sensation and concepts is determined by the difference in structure of their tools; i.e., the difference between the structure of the forms of intuition on the one hand and that of the forms of thinking on the other. This structural difference is manifest in the nature of the relation of the particular to the universal in the respective domains of sensation and concepts. In terms of this relation, the difference between the factors is determined, first of all, by the question, which of the related terms — the particular or the universal — is primary in their respective domains. Conceptualization presupposes the particular as a primary datum.