Although Descartes is often said to have coined the modern notion of ‘consciousness’, he defines it neither explicitly nor implicitly. This may imply (1) that he was not the first to use ‘conscientia’ in its modern, psychological sense, or (2) that he still used it in its traditional moral sense. In this paper, I argue for the latter assumption. Descartes used ‘conscientia’ according to the meaning we also find in texts of St. Paul, Augustine, Aquinas and later scholastics. Thus the (...) Cartesian conscientia is, technically speaking, a shared knowledge of the specific value of our thoughts as thoughts and at the same time the cause of this value. This means that it is not itself a kind of individual knowledge, awareness, or a particular thought. Rather, ‘conscientia’ refers to the evaluative knowledge of an ideal observer. (shrink)