1. To kill a Mockingbird.

  2. To catch a thief.

  3. To catch a cheater.

Why is "to" used in this examples what does this phrases mean? I am unable to interpret any of these phrases.

  • 5
    Note: These are not "sentences;" these are but short phrases and titles. (I think the question is still an interesting one, but I also think the distinction is rather important.)
    – J.R.
    Commented Sep 29, 2019 at 9:46
  • 1
    These are just phrases with infinitives; "To wash my clothes" being another. “To Verb a Noun” or verbing a noun actually means something entirely different, it means turning a word that is usually used as a noun (/noun-phrase), into a verb, usually in a linguistically dubious and/or faddish way, perpetrated by management types: "to baseline the performance data", "to calendar the meeting", "to action the tasks" The Basics of Verbing Nouns
    – smci
    Commented Sep 29, 2019 at 21:13
  • 1
    Bonus points if you manage to split the infinitive: "To boldly go where no man has gone before" [Star Trek]. (Splitting an infinitive used to be considered ungrammatical, but that's now accepted)
    – smci
    Commented Sep 29, 2019 at 21:15
  • 2
    To Kill a Mockingbird is the title of a book, referring to the narrator's father's(?) remark that “it is a sin to kill a mockingbird,” making that sin a metaphor for the central sin of the story (I guess). Similarly, To Catch a Thief is the title of a movie, alluding to the proverb “Set a thief to catch a thief,” because the movie's plot is about recruiting a former thief to act as detective to solve a crime. Commented Sep 29, 2019 at 22:03
  • @smci The OP's title is not referring to the transitive verb to verb, it's merely using verb as a wildcard representing any verb. Commented Sep 29, 2019 at 22:07

3 Answers 3


None of those three phrases is a sentence.

In those phrases, the word to means that the following verb is an infinitive. It prevents the reader from interpreting the word as an imperative verb. For example, the following two sentences are commands; they tell the reader to do something:

Kill a mockingbird.

Catch a thief.

"To kill a mockingbird" is actually a noun. It denotes the action without making a statement, command, or question. Here is a sentence where it serves as the subject:

To kill a mockingbird is a sin.

The verb in that sentence is "is". The subject is "To kill a mockingbird"—that kind of action. The sentence states that the action is a sin.

More commonly, we would word the sentence like this:

It is a sin to kill a mockingbird.

You could also word it with a gerund instead of an infinitive:

Killing a mockingbird is a sin.

Infinitives introduced by to are very common in English. Here is where the phrase "to kill a mockingbird" first occurs in the novel by Harper Lee. I've marked all the infinitives that are introduced by to:

Atticus said to Jem one day, "I'd rather you shot at tin cans in the back yard, but I know you'll go after birds. Shoot all the blue jays you want, if you can hit 'em, but remember it's a sin to kill a mockingbird." That was the only time I ever heard Atticus say it was a sin to do something, and I asked Miss Maudie about it. "Your father's right," she said. "Mockingbirds don't do one thing but make music for us to enjoy. They don't eat up people's gardens, don't nest in corncribs, they don't do one thing but sing their hearts out for us. That's why it's a sin to kill a mockingbird."

The word to can serve this function for any English verb or verb phrase. For example, here is another quotation, by David Attenborough:

The only way to save a rhinoceros is to save the environment in which it lives.

Each phrase starting with "to save" names an action, and the sentence says something about these actions. The word "to" is needed to make a noun phrase that denotes the action of the verb "save" without claiming that the action happened. The word "save" functions as a verb in this sentence: "We saved a rhinoceros." This sentence doesn't say something about saving a rhinoceros, it says that a rhinoceros was saved. Similarly, the sentence "Save a rhinoceros today!" is a command, not a statement about saving a rhinoceros.

  • So "To kill a mockingbird" is a noun which describes the action of killing a mockingbird?
    – ikigai20
    Commented Sep 29, 2019 at 9:21
  • 2
    @lollel123 Yes. I'll add another quotation to illustrate. (People who are fussy about terminology might call it a "noun phrase". The important thing to understand is that the phrase serves as a name for the action of the verb, so you can talk about the action instead of claiming that the action happened.)
    – Ben Kovitz
    Commented Sep 29, 2019 at 10:17
  • "To kill a mockingbird" is actually a noun phrase. No it's not. If it were a noun phrase you'd be able to: pluralise it, add an article, add an adjective. But you can't. These diagnostic tests show us it's not a noun phrase. Commented Sep 30, 2019 at 6:59
  • What is the difference between "to kill a mockingbird" and "killing a mockingbird".
    – ikigai20
    Commented Sep 30, 2019 at 9:35
  • @curiousdannii It sounds like you're using a different terminology: one common among linguists, which defines 'noun', etc. in terms of syntactic rules. I'm using the familiar, traditional terminology, where 'noun' is defined by its grammatical role in a sentence (naming rather than claiming, explained above).
    – Ben Kovitz
    Commented Oct 3, 2019 at 21:35

This “to” is necessary to show that these sentences are about more general actions, for example, about a task for someone. This is an indefinite form of the verb.


Sentences starting "To [do something]"are usually followed by instructions on how to achieve the action. For example.

To catch a thief, examine the CCTV tapes


To bake a cake, collect the ingredients, flour, eggs, sugar, and so on ....

"To Kill a Mockingbird" is an exception, being the title of a book and a film, although it could be followed by instructions for avicide.

  • 2
    What you have said is correct; however, more often than not, such phrases are found later in the sentence (for example: Here are some tips a teacher might use to catch a cheater).
    – J.R.
    Commented Sep 29, 2019 at 10:33

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