Alan Jacobs explains the insoluble problem faced by humanities departments:

1) The scholarly performance of academic humanists is evaluated -- by colleagues, tenure committees, etc. -- using criteria developed for evaluating scientists.

2) Those criteria are built around the idea of knowledge creation.

3) But many humanists aren't sure what counts as knowledge creation for them, since they are not able to follow any agreed-upon method for testing hypotheses.

4) This problem grows more pressing as expectations for publication rise: scholars are asked
to create more and more knowledge without being sure what knowledge is.

5) Thus the Cycle of Theory, in which an approach to doing humanist work arises, is deemed outrageous, is more and more generally accepted, becomes orthodoxy, is challenged by a new approach, and becomes superannuated. See: the New Criticism, archetypal criticism, structuralism, deconstruction, the New Historicism, Queer Theory, eco-criticism, etc. Lather, rinse, repeat.

In another post, Professor Jacobs describes his effort to teach English in an age of rapidly changing technologies. It's well worth a read.