This dissertation examines the significance of Johann Nikolas Tetens, a German empiricist philosopher working in the 1770's, to the theoretical philosophy of Immanuel Kant. I begin by examining Tetens' discussion of philosophical methodology in his 1775 essay \textit{Über die allgemeine speculativische Philosophie}. I make the case that Tetens' criticism of the methodology of the Scottish common sense philosophers and his subsequent attempt to incorporate what he takes to be their valuable insights into the approach of the broadly Wolffian philosophical tradition (...) provides important context for interpreting Kant's methodology in the \textit{Critique of Pure Reason}. I then examine two different cases of Tetens' applying this methodology in his 1777 text \textit{Philosophische Versuche über die menschliche Natur und ihre Entwickelung}. I argue that Tetens' discussion and critique of Humean causation in the fourth essay of the \textit{Philosophische Versuche} heavily influenced Kant's understanding of ``Hume's Problem'' and that many of the more obscure issues about the Kant-Hume relationship can be greatly clarified by giving sufficient attention to Tetens. I then examine Tetens' engagement with Thomas Reid's account of perception. I argue that Tetens' attempt to develop a representationalist account of perception which withstands Reid's objections leads him toward the view that representation requires object concepts and the problem of accounting for the origin of these concepts pushes Tetens to articulate an account of synthesis. In the final chapter, I examine Kant's proof that the real of appearances has intensive magnitude in the Anticipations of Perception. I raise several difficulties for the interpretation of the proof and then argue that Tetens' discussion of perception can provide us with the context for such a proof and the nature of the ``correspondence'' between sensation and objects. (shrink)