will first explain Kant’s account of schemata in the Schematization of the Pure Concepts of Understanding, and subsequentlypresent his argument against idealism in hisRefutation of Idealism.

In the former, Kant wants to show how concepts canbe applicable to appearances. To answer this, he thinks a transcendentaldeduction of judgment is necessary. Kant introduces the notion oftranscendental schema.

A schema is both sensible and intellectual, and originatesin our imagination. The application of a concept to an appearance requires a transcendentaldetermination of time, which entails both pure concepts of the understanding andappearances, and serves as the schemata which negotiates the inclusion ofappearances under pure concepts. Schemata serves as the foundation of sensibleconcepts in place of images, and are rules which determine how a prioriconcepts can be applied to appearances.

The schema for concepts derived fromthe senses exist solely in thought, whereas the schema of concepts not derivedfrom senses exist as pure synthesis. Without schemata of the sensibility, thecategories could not arise, but such schemata at the same time limits their application to the sensibility. In the latter, Kant sets out to prove, contra Descartes’ problematic idealism, that we have real experience, not just imaginaryexperience. He claims that we can know that external things existby virtue of knowing that we have internal experiences. We have knowledge ofour existence in time, and our conception of time presupposes our consciousnessof permanence.

Such permanence is not to be found within us, for permanence iswhat allows us to acquire the knowledge of our existence in time. In order for usto be conscious of permanence, it is necessary that permanent things externallyexist, and our knowledge that we exist in a temporal order is possible only if externalthings exist. Ultimately, the perception of our own existence is also aperception of external existence.