This volume presents a series of essays which investigate the nature of intellectual inquiry: what its aims are and how it operates. The starting-point is the work of the American Pragmatists C. S. Peirce and John Dewey. Inquiry according to Peirce is a struggle to replace doubt by true belief. Dewey insisted that the transformation was from an indeterminate situation to a determinate or non-problematic one. So Isaac Levi's subject is changes in doxastic commitments, which may involve changes in attitudes or changes in situations in which attitudes are entangled. The question what justifies modification of doxastic commitments is a normative one, and so may not be understandable in purely naturalistic terms.