He is known for his detailed exegesis and interpretation of the philosophy of Ludwig Wittgenstein, his critique of cognitive neuroscience, and for his comprehensive studies of human nature.

"[3] He believes that empirical observation and research is a categorically distinct kind of activity from conceptual investigation and clarification, even though there is sometimes no sharp dividing line between the two.

It follows that scientific inquiry (learning more facts about humans or the world) does not help to resolve them anymore than discoveries in physics can help to prove a mathematical theorem.

The first volume The Categorial Framework: a Study of Human Nature surveys the most general concepts: substance, causation, powers, agency, teleology and rationality, mind, body and person.

The second, The Intellectual Powers: A Study of Human Nature investigates consciousness, intentionality and mastery of a language as marks of the mind.

This is followed by detailed logico-grammatical studies of human cognitive and cogitative powers, ranging from perception through knowledge and belief to memory, thought and imagination.

Hacker's methodology is connective analysis in which the wide range of conceptual and logical features of the relevant subjects is laid bare [vague].

Hacker has frequently collaborated with fellow Oxford philosopher G. P. Baker, and Australian neuroscientist Max Bennett.