Schemas are specifications or conventions that tell both you and the other what means what.
Can be also refered by the term vocabularies
In any event, Kant's idea of a "schema", when translated to our current understanding, is something like "the fundamental, intuitive ordering principle which people use to establish categories, whether mental, sensory, or 'transcendental'." For instance, the category of "quantity" must be ordered by number; thus, "number" is the "schema" of the mental category we understand as "quantity".

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