A great blog on usage of the ‘copular’ verb-forms.
Here’s an extract (and, yes, I know that ‘is’ as a contraction should not have been used in that particular sentence, considering the subject matter of the blog/essay)

“Some while ago, I attempted to write an essay on the uses and abuses of is and its cohorts are, was, were, be, being, been, seems, and becomes in poetry. I set out to do so without ever using the word except as the word. I could talk about the meaning symbolized by those two random symbols—i and s—but I could not use is as a sentence verb.I had no idea how difficult doing so would be. It required that I revise sentence after sentence, struggle to find active ways to express state-of-being ideas. Eventually, however, I succeeded; the chapter is titled “Compression III—Linking Verbs” in The Art and Craft of Poetry Borgo/Wildside, 2009. And I think it makes the point I wanted: writing can become stronger and more energetic without the linking or copular verbs.But not always.”

via Collings Notes: To “Is,” or Not to “Is”…Or Perhaps to Do Both.