In Descartes’ corpus, the term “sensation” (from the Latin sentire) always concerns senseperception (cf. AT VIIIA 316; CSM I 280). (Indeed, it refers to human sense perception; this clearly raises issues concerning sense perception in nonhuman animals, treatment of which is beyond the scope of this article.) This point bears emphasis because many Anglo-American philosophers today make a distinction between sensation and sense perception; in fact, what these philosophers refer to as sensations (e.g., pain, hunger, thirst) will for Descartes be connected to what he calls the internal senses (AT VIIIA 316–18, CSM I 280–81; the internal senses are seldom thematized in the Descartes literature: see Baker and Morris 1996, esp. 124ff.). The internal senses, as we will see, have a special role vis-à-vis the mind-body union and, because of this, a special role vis-à-vis Descartes’ claim that sensations are confusedmodes of thinking.

1.Internal and External Senses

The internal senses are part of the traditional Scholastic package of functions of the sensitive soul (although Descartes’ characterizations differed from those of his predecessors), functions that Descartes sought to explain mechanically – that is, without a soul (see dualism and perception). The internal senses are distinguished from the external ones in virtue of the fact that their “objects” are, in some sense, properties of the percipient'sbody rather than (in some sense) properties of things outside the body. Descartes identified two internal senses, connected with the natural appetites and the emotions respectively (AT VIIIA 316, CSM I 280; the present entry concentrates on the first internal sense, that associated with the natural appetites; see passions for a treatment of the second internal sense). The “objects” of the internal senses (e.g., pain, hunger, thirst, fear, anger, joy) are intrinsically connected with bodily health or welfare. To be sure, the “proper purpose” of all sensory perceptions is “simply to inform the mind of what is beneficial or harmful for the composite of which the mind is a part” (AT VII 83, CSM II 57; Simmons [2001] stresses that this is a teleological account of sensory perception and defends Descartes against the charge of inconsistency with what is widely seen as his opposition to teleological explanation).