Can you start a sentence with 'it'? Of course. Do you want to? Maybe not.
It never ceases to amaze me how much bad grammar information is out there. For example, here’s a question a professional editor asked me a while back: “Is it true you can’t start a sentence with “it”?
We were at a conference, standing in a busy hallway among other people waiting to ask questions. So I didn’t have the time to ask: Where’d you hear that? What’s the thinking behind it? Have you actually followed that advice in your editing work?
There are a lot of people who’ve heard you can’t start a sentence with “and,” and many who’ve heard the same about “but” and “so.” Those prohibitions are fictional (In fact, “Garner’s Modern American Usage” calls the idea that you can’t start a sentence with “and,” “but,” or “so” a superstition). But the alleged “it” rule was a new one on me.
My answer was short: “It’s fine,” I said, not realizing until afterward that my answer was an example.
“It” is a pronoun, like “he,” “him,” “we,” “us,” “they,” “them,” etc. Pronouns head up sentences all the time. She is in the yard. I am in the yard. They are in the yard. It is in the yard.
So the answer was easy. But a few hours later I was thinking about the question and had a realization: The supposed rule, though wrong, might actually be rooted in a useful idea.
Look at the sentence, “It is John who ate the last piece of cake.” This is perfectly grammatical. The main subject is “it,” the main verb is “is.” The “Oxford English Grammar” calls this “the cleft it,” in which “the sentence is split to put the focus on some part of it.”
Compare that sentence with the simpler “John ate the last piece of cake” and you can see how “it is John” adds a different emphasis. But that emphasis comes at a price: extra words and the loss of vividness you get every time you replace a tangible subject and action-oriented verb like “John ate” with more the abstract “it is.”
In news writing especially, “John ate the last piece of cake” is considered better form than “It is John who ate the last piece of cake.”
I bet that’s the origin of the myth that plagued our editor friend.