Is science the only way of knowing?

An economist friend of mine recently recommended Peter Boghassian's book Fear of Knowledge: Against Relativism and Constructivism. I had heard of the book, but my friends very high recommendations of it prompted me to order it. 

My friend and I had been discussing the issue of "critical thinking skills" and how much of the movement that has developed around this concept has been co-opted by postmodernist thinkers.

Since I had to wait for snail mail, I looked the book up at Oxford University Press. Obviously I can't adequately assess the book until I get it, but I notice that the summary at Oxford indicates that that his main line of argument is that postmodernists that postmodernists assume science is not the only way of knowing the world.

This chapter introduces a thesis that is enormously influential in the contemporary academy – Equal Validity: there are many radically different, mutually incompatible, yet ‘equally valid’ ways of knowing the world, with science being just one of them. It explains in a general way how constructivist views of knowledge might be thought to underwrite this thesis.

Boghassian presumably argues against this thesis. Of course, on this particular thesis, I would find myself on the side of the postmodernists. There are clearly other ways of knowing than science. Science could never have been developed if there weren't. 

I have addressed this issue a number of times, including here, here, and here.

Now this doesn't necessarily affect the usefulness of Boghassian's arguments against the postmodernists. In fact, this is the interesting thing about arguments between modernists (of which Boghassian is one) and postmodernists: They're both right in many of their critiques of each other. Modernists limit their toolbox to only one tool, and postmodernists seem to reject limits altogether. 

The holes in modernism's epistemological net exclude things that should not be excluded and the holes in postmodernism's net are so big they let too many things through.

It seems to me many scholars like Boghassian use the word "science" in the same way that they charge postmodernists use "knowledge" or even "thinking skills," that is to say, without clear definition.

If you define science narrowly--as that method by which the hard sciences come to their conclusions, then you exclude universally acknowledged forms of reasoning (such as those practiced by philosophers like Boghassian) that, of necessity, he must himself practice in his critique of postmodernism. And if you define it so broadly as to encompass rational inquiry in general, then to call it "scientific reasoning" is misleading, since it implies only that form of reasoning used in the hard sciences is valid.

In fact, asserting that "scientific reasoning is the only valid form of reasoning" is itself vulnerable to the argument against postmodernism Boghassian apparently uses in one of his chapters; namely, that the assertion is a performative contradiction: If the assertion "scientific reasoning is the only valid form of reasoning" is true, then scientific reason cannot be the only valid form of reasoning since there is no way to arrive at that conclusion using scientific reasoning (unless, again, your definition of scientific reasoning includes all forms of rational inquiry, which, again, is misleading).

In any case, I await the book.