noesis

Noesis is a term used in philosophy and cognitive science to denote a mental act of cognition, perception, or thought. It is often contrasted with noema, the object or content of that act, particularly in phenomenology, where the relationship between consciousness and its objects is analyzed through intentional acts.

In Husserlian phenomenology, noesis refers to the active process of consciousness by which experiences are grasped, such as perceiving, imagining, judging, or remembering. Noema, by contrast, is the object as it is intended or given in experience. The noesis-noema distinction helps describe how phenomena are constituted in consciousness and how meaning arises through subjective acts, independently of external objects as they exist independently of perception.

Historically, the term derives from the Greek νοησις (noēsis), meaning thought or intellect. In ancient and medieval philosophy, related terms and concepts concerned the faculties of the mind and the nature of understanding, although the precise usage varies across authors. In contemporary philosophy, noesis remains primarily associated with phenomenology and philosophy of mind, where it denotes the experiential or cognitive act rather than the external thing itself.

In modern discussions, noesis can also appear in cognitive science and psychology as a general label for mental acts such as perception, reasoning, or decision-making. While the term is less common in empirical work today, it continues to appear in analytic and continental traditions as a way to differentiate processes of mental activity from their intentional content.

See also: noema, intentionality, phenomenology, nous.