Is there a specific group/category of words that I can look for before/after "its/it's" to determine proper/improper usage?

I'm asking this for the purpose of writing code that corrects the usage of "its/it's", however this isn't a question for programmers, but rather for English specialists.

I'm looking for some category or group or type of words that can accurately and reliably identify the proper usage.

For example:

This bike is popular [because of] its [quality] | [but] it's [not] very affordable.

It seems that there may be a pattern / word-group that I can look for surrounding "its" or "it's" to determine that it's correctly / incorrectly used.

  • You might download a corpus and build yourself some n-grams for Bayesian analysis. COCA is pretty popular around here. Though I'm sure you could catch 90%+ of the cases that way, I imagine the devil will be in the details (edge cases), as always.
    – Dan Bron
    Commented Oct 31, 2014 at 21:45
  • @ArsenY.M. what if I edit my question to ask for only a small level of assurance rather than full accuracy. If I could just figure out a trick to know for sure only some of the time that'd be great.
    – J.Todd
    Commented Oct 31, 2014 at 21:50
  • 1
    Maybe a simple answer is that its should be followed by a noun phrase, while it's should be followed by an adjective or verb (optionally preceded by not and adverbs).
    – Barmar
    Commented Oct 31, 2014 at 21:58
  • 1
    jtodd: I don't know for sure, but I'd bet money the "patterns" you seek will exhibit a far greater variance than perhaps you're envisioning. Any small set of words we can think of, off the top of our heads, will probably let you catch maybe 2% of cases total, and will be dead wrong (ie will give the opposite advice) in other similar cases we haven't considered. From your users' perspective, providing this 2% assurance would actually be worse than doing nothing, because they'll assume if you don't tell them they're wrong, they're right.
    – Dan Bron
    Commented Oct 31, 2014 at 21:59
  • @DanBron if thats the case, I'd still like to see the explanation in an answer, even if it's preceded by "No."
    – J.Todd
    Commented Oct 31, 2014 at 22:00

1 Answer 1


Since its is a possessive, it should normally be followed by a noun phrase -- you can't own a verb or adjective. The noun may be preceded by adjectives, which may be modified by adverbs. But there shouldn't be an article before it -- you say its color, not its the color.

Since it's is a contraction of it is, it should be followed by a phrase that can be used after the verb to be. This can be an adjective, optionally preceded by adverbs, when describing a quality that the object possesses. It can be a verb phrase, to describe something that the object is doing, or idioms like it's going to rain. It can also be a noun phrase beginning with an article, when describing what the object is, as in it's a book.

However, it's can also be followed by a noun phrase that doesn't start with an article, as in it's Fred's book or it's Washington, D.C. (the answer to the question What's the capital of the US?). It can also be followed by mass nouns, as in it's water, a noun phrase beginning with a determiner, as in it's his book. There are some special cases, such as

What's your favorite class in school? It's math. What's your favorite sport? It's football.

But you'll have to be very careful about some of this, because verbs can often be used as adjectives. Both of these are correct:

It's running late (referring to a train that's behind schedule)

Its running time is 90 minutes (referring to the length of a movie)

  • In other words, those involved in developing grammar checking in high-end document editors deserve raises.
    – J.Todd
    Commented Oct 31, 2014 at 23:04
  • 1
    @jt0dd Assuming they get it right. :)
    – Barmar
    Commented Oct 31, 2014 at 23:06
  • Quasi-articles: “What’s making that noise?” → “It’s this rocking chair.” Collective/mass nouns: “What’s this liquid?” → “It’s water.” Gerunds (if you count them as nouns): “What’s your favorite form of exercise?” → “It’s swimming.” See When can an article be omitted? (on ELL). Commented Oct 31, 2014 at 23:17
  • @Scott Good points. The "quasi-articles" case generalizes to other determiners: it's his book.
    – Barmar
    Commented Oct 31, 2014 at 23:22
  • I left that out because "Fred's" is already an example of a possessive. Commented Oct 31, 2014 at 23:24

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