Alfred North Whitehead, answered from the texts and cited to the page.
Speculative philosophy is the endeavour to frame a coherent, logical, necessary system of general ideas in terms of which every element of our experience can be interpreted.12 By "applicable" I mean that the system applies to some matters of experience; by "adequate" I mean that there are no matters of experience to which the system fails to apply.
The criteria are coherence, logical consistency, applicability, and adequacy. The method is imaginative generalization — the leap from the observation of some range of fact to a generalized hypothesis whose range of applicability is then tested. The danger is overstatement: the unwarranted generalization of categories drawn from a restricted region (Cartesian subject-object analysis, Newtonian space-time, Lockean primary-and-secondary qualities) into purported features of the most general nature of things.
Such overstatements commit the fallacy of misplaced concreteness: mistaking the abstraction useful for some purposes for the concrete actual. The proper response is not to abandon speculative philosophy in favour of the cataloguing of ordinary language or the analysis of scientific propositions; the proper response is to do speculative philosophy with discipline — to frame schemes that aim at coherence and adequacy, to test them against the widest range of experience, and to revise them when the test fails.
The positivist rejection of metaphysics is itself a metaphysical position: it presupposes a verificationist account of meaning that cannot be verified by its own criterion, and it imports unexamined commitments about what counts as experience. The contemporary analytic metaphysics that has reasserted itself since the Quinean turn is doing something closer to speculative philosophy than its practitioners always acknowledge.3
By this notion of 'interpretation' I mean that, everything of which we are conscious, as enjoyed, perceived, willed, or thought, shall have the character of a particular instance of the general scheme. Thus the philosophical scheme should be coherent, logical, and, in respect to its interpretation, applicable and adequate.Process and Reality, pp. 5–6
SPECULATIVE PHILOSOPHY SECTION I. Speculative Philosophy; Coherent, Logical, Necessary System of Ideas; Interpretation of Experience. tif Defects of Insight and of Language; Conditions for Observation; Rigid Empiricism, Imagination, Generalization; Coherence and Incoherence; Creativity, the Ultimate. III.Process and Reality, pp. 3–4
For example, Hume assumes that his doctrine of association holds for all types of impressions of sensation and of ideas of them indiscriminately. This assumption is part of his theory.Adventures of Ideas, p. 285
The methodological credo that opens Process and Reality. The position was deeply unfashionable from the 1930s through the 1960s — the era of logical positivism (Carnap, Ayer), of ordinary-language philosophy (the later Wittgenstein, Austin), of the rejection of metaphysical "pseudo-problems." The Quinean turn ("Two Dogmas" 1951; Word and Object 1960) softened the positivist consensus and reopened space for ontological commitment. The contemporary analytic-metaphysics revival (Kit Fine, Theodore Sider, Jonathan Schaffer) does work that is structurally close to speculative philosophy though usually framed differently. The continental revival of speculative philosophy (Stengers's Thinking with Whitehead 2002, the speculative-realist movement of the 2000s — Meillassoux, Harman) has reclaimed the method explicitly. The disagreement now is not whether speculative philosophy is possible but what its disciplinary constraints are and how it relates to the empirical sciences.