Descartes speaks of judgment in three closely related ways. Fundamentally, he conceives of judgment as the act of will in assenting to some matter (or dissenting from it), that is, affirming or denying that something is the case: “The act of judging [actum judicandi] itself consists simply in assenting (i.e. in affirmation or denial)” (AT VIIIB 363, CSM I 307). This fundamental conception gives rise to two further notions. One is of judgment as a faculty – the mental faculty by which minds form judgments qua acts of assent: for example, “I know by experience that there is in me a faculty of judgement [judicandi facultatem]” (AT VII 53, CSM II 37). The other notion is of judgments as propositions – the propositions affirmed or denied when minds form judgments qua acts of assent: for example, “it is not easy for the mind to erase these false judgements from its memory” (AT VIIIA 36, CSM I 219). The description that here follows focuses on the first, and more fundamental, of these three conceptions.

Judgments arise from a cooperation of the intellect and the will. According to Descartes, the mind's operations fall into two main kinds: “All the modes of thinking that we experience within ourselves can be brought under two general headings: perception, or the operation of the intellect, and volition, or the operation of the will” (AT VIIIA 17, CSM I 204). The division of labor is as follows. The intellect is responsible for cognition of the contents that get judged. Its operation in judgment involves perception or awareness of those contents: “All that the intellect does is to enable me to perceive the ideas which are subjects for possible judgements” (AT VII 56, CSM II 39). The will is responsible for the judgmental attitudes adopted toward the contents perceived. Its operation in judgment “simply consists in our ability … to affirm or deny” those contents (AT VII 57, CSM II 40). Though both the intellect and the will are involved, strictly speaking judgment is the act of will – “I assigned the act of judging itself … to the determination of the will rather than to the perception of the intellect” (AT VIIIB 363, CSM I 307).