George Scialabba on the New York Intellectuals (from What Are Intellectuals Good For – which, sadly, seems to be out of print):

Their primary training and frame of reference were the humanities, usually literature or philosophy, and [they] habitually, even if often implicitly, employed values and ideals derived from the humanities to criticize contemporary politics...They were generalists: they drew, from a generally shared body of culture, principles of general applicability and applied them to facts generally available. Their "specialty" lay  not in unearthing generally unavailable facts but in penetrating especially deeply into the shared culture, in grasping and articulating its contemporary moral/political relevance with special originality and force.

Paul J. Griffiths, distinguishing intellectuals from dilettantes ("Letter to an Aspiring Intellectual,“in First Things, a few years ago):

Perhaps you’ll be a dilettante: You’ll love what you think about and you’ll think hard about it, but you’ll be easily bored and won’t think about anything for long. You’ll read many things and (perhaps) write many, but you’ll read and write about disparate topics, and once you’ve read for a while about something, and perhaps written about it, you’ll move on to something else. Clever people—quick studies—are often like this. They have properly intellectual gifts, but they lack the patience for attention’s long, slow gaze (on which see below), and so their intellectual life coruscates, sparking here and there like a firefly on the porch, but illuminating nothing for long...I’d like to warn you against this tendency [because] the extent to which you embrace dilettantism is just the extent to which you won’t do serious intellectual work.