Tetens' Critique of Reid on Perception and the Problem of the Transcendental Deduction

The influence of Thomas Reid and his account of perception is easily felt throughout many of the discussions that occur in Johann Nikolaus Tetens' Philosophische Verusche über die menschliche Natur und ihre Entwickelung (1777).  Tetens favorably discusses Reid's account of perception in numerous places and makes it quite clear that he accepts several aspects of Reid's account. Tetens seems to have been heavily influenced by Reid's account of sensations as non-intentional states that do not resemble objects, his distinction between sensation and perception, and his account of sensations as natural signs.  However, there are two particularly odd features of Tetens' discussion of Reid. First, despite accepting these Reidian doctrines, Tetens bluntly dismisses Reid's attack on the theory of ideas without feeling the need to provide an argument against it.  Second, in the fourth essay of the Philosophische Versuche, Tetens cites Reid's view that the sensation of hardness does not resemble the quality of hardness in the body, but then raises the very peculiar question of whether or not the sensation could still be the material for the idea. 

I want to suggest that this peculiar question from Tetens is a reference to Reid's experimentum crucis discussion in the chapter on touch in the Inquiry where he argues that sensory experience is unable to account for the origin of our notion of extension.  I will argue that when close attention is paid to some broader methodological criticisms that Tetens articulates about common sense philosophy, both the absence of a direct defense of the theory of ideas from Reid's objections and his peculiar question can be explained.  Instead of an opponent to be refuted, Tetens takes Reid to be presenting two serious explanatory challenges for his own account of mental representation: (1) the challenge of showing that a version of the theory of ideas can survive the Reidian criticisms, and (2) the challenge of accounting for object concepts that seemingly cannot have their origin in sensory experience.  These challenges are taken up in the fifth essay of the Philosophische Versuche, where Tetens sketches out an account of how the representation of objects is made possible by concepts which are formed by attending to relations that obtain between sensations which are unified by the mind and brought to awareness. Ultimately, in trying to meet these challenges, Tetens is forced to acknowledge the limitations of sensation and has to shift most of the explanatory burden onto more active mental faculties.  In this discussion, Tetens not only anticipates the general problem that Kant would address in the Transcendental Deduction, but also provides a rough outline of what a potential solution might look like.