Gilbert Harman

Putnam rejects "metaphysical realism," which takes "the world" to be a single complex thing, a connected causal or explanatory order into which all facts fit. he argues that such metaphysical realism is responsible for views he finds implausible; in particular, it can lead to moral relativism when one tries to locate the place of value in the world of fact. i agree that metaphysical realism will lead a thoughtful philosopher to moral relativism, but find neither of these views implausible. in particular, putnam's main argument against metaphysical realism seems fallacious and his suggested alternative, to think of truth as the idea limit of rational inquiry, is clearly incorrect.

Harman distinguishes between two uses of the term “logic”: as referring either to the theory of implication or to the theory of reasoning, which are quite distinct. His interest here is reasoning: a process that can modify intentions and beliefs. To a first approximation, theoretical reasoning is concerned with what to believe and practical reasoning is concerned with what to intend to do, although it is possible to have practical reasons to believe something. Practical considerations are relevant to whether to engage in theoretical inquiry into a given question, the extent of time and other resources to devote to such inquiry, and whether and when to end such inquiry. Simplicity and conservatism play a role in theoretical reasoning that can be given a practical justification without allowing wishful thinking into theoretical reasoning, a justification that can also be given a non-practical interpretation.