A frustrating, challenging, and deeply insightful book. In every chapter, Dewey is at pains to demonstrate insights about the nature of many philosophical topics by drawing on his instrumentalist, operationalist, functional theory of inquiry. Because of this, there is a lot of repetition and reformulation of the same ideas. It could probably have been a much shorter book, but then the points that Dewey wants to demonstrate would have been more easily overlooked.
On my reading of the book, I take away three absolutely essential points:
(1) The general structure of inquiry, from a problematic -- indeterminate, unclear, unintelligible, incoherent -- situation, to a resolution of the problem by instituting a determinate -- unified, clear, intelligible, coherent -- situation. All inquiries move from felt indeterminacies in a situation, to a determinate situation.
(2) The function of both selected existential materials (or facts of the situation) and conceptual materials (or procedural means) in overcoming a problematic situation. Bringing these two functionally distinguished elements together, by using conceptual materials to direct operations for experimenting on existential materials, into a coherent whole is what provides a solution to a problem, instituting a determinate situation.
(3) The role of *intelligence* as specified by the means-consequence relation. The means-consequence relation specifies the instrumental meaning of things, through their figuring as means to bringing about specific consequences or as consequences of operating on specific means. This is especially interesting in relation to Dewey's claim that actions and operations are "universal", providing a kind of master argument for pragmatism, since kinds are not identifiable independently of their role in activities. Dewey thus provides a theory of the pragmatic or operational a priori through this relation.
On this last point, there is some uncertainty about whether the means-consequence relation overlaps with the so-called "conceptual materials/procedural means", or is supposed to be broader than this.
Inquiry is, at heart, both practical and conceptual. Conceptual materials are directive of operations to be performed on existential materials, to perform experiments guided by procedures and ideas that have proven themselves in past inquiries. In the end, inquiry is a matter of doing things intelligently: science too develops by articulating and testing practical inferences at a general level, which bottoms out in operations on stuff in the world.
We learn not only facts, but about how to conduct inquiry better. Methods emerge organically from past successful inquiries, providing both the means to guide future inquiries and normative standard of success. There is thus an iterative process of method-learning, which also is the basis for the selection of relevant existential materials.
Dewey also expresses interesting pluralist ideas at various points in the book, which have become independently popular and important in contemporary philosophy of science. Well worth reading for contemporary philosophers concerned with the nature of inquiry, both in philosophy of science and in "zetetic" epistemology.