What is the Zero (or Bare) Infinitive?

The zero infinitive is a type of complement with an infinitive verb form that's not preceded by the particle to. Also known as the bare infinitive.

The zero (or bare) infinitive is used after verbs of perception (see, feel, hear), many auxiliary verbs (may, should, must), the verbs make and let, and the expressions had better and would rather. Contrast with the to-infinitive.

See Examples and Observations below. Also see:

• Exercise in Identifying Infinitive Phrases
• Passive Infinitive
• Ten Quick Questions and Answers About Verbs and Verbals
• Verbals
• What Are Grammatical Zeros and Bare Relatives?
• What Is a "Split Infinitive" and What's Wrong With It?

Examples and Observations

• I didn't want to eat the crawfish. My sister made me try it.
• Several witnesses saw the boy leave the sidewalk and run into the side of the bus.
• "I remember the first song I heard him sing: 'Mention Dirty to My Heart.'"
  (Alan Lomax speaking about Woody Guthrie)
• On Tuesday, the White House announced new steps to expand research into technology that would help capture and store carbon emitted by burning coal.
• The program has strengthened our economy and helped remedy past and present discrimination.

Verbs That Can Appear in Bare infinitives

• "[I]t is sometimes possible to omit the infinitive marker to for the sake of a more harmonious-sounding construction. Grammarians call such infinitives without markers bare infinitives. The English language only allows us to omit the marker in infinitives placed after certain verbs in the active voice.
  "The following list of sentences illustrates a few of the verbs after which we may omit the infinitive marker. The verbs in italics are the verbs to note (they have been written again in parentheses in their present indicative forms at the ends of the sentences.) The words in bold are bare infinitives. The marker to is missing in each. Read every sentence twice, first without the marker and then with the marker restored. The bare versions are clearly preferable. . . .
  I felt her heart beat. (feel)
  We heard the birds whistle a merry tune. (hear). . .
  When these verbs are used in the passive voice, the marker to returns. . . . Her heart was felt to beat. (feel)
  The birds were heard to sing a merry tune. (hear) . . .
  (M. Strumpf and A. Douglas, The Grammar Bible. Owl Books, 2004)

How to Recognize Zero or Bare Infinitives

• "One way to figure out whether a verb is a bare infinitive or not is to simply remember that a modal is always followed by a bare infinitive, no matter how many verbs are in the verb string. Another way to tell whether you have a bare infinitive or not is to replace the verb with another verb whose infinitival form is different from its present tense form. Be is a good choice; the bare infinitival form of be is, well, be. The present tense forms of be are completely different (in many English dialects): is, am, are. So, if we can replace a verb (such as remain, grow, appear, or become in the following example) with be, that means that those verbs, like be, are bare infinitives.
  We watched Leo remain/grow/appear/become silly.
  We watched Leo be silly."
  (Anne Lobeck and Kristin Denham, Navigating English Grammar: A Guide to Analyzing Real Language. Wiley, 2013)

On the Increasing Use of Bare Infinitives

• "[T]he overall trend observable in the corpora, namely increasing use of bare infinitives, seems to be the result of two parallel developments . . .. There is a slow but general groundswell in favour of the bare infinitive which affects all varieties of English (written and spoken, British and American) and both constructions (help with object, help without object). Superimposed on this, and largely confined to writing and formal and elaborate speech, there is a more specialized development, namely the spread of the specific constructional type (to) help + bare infinitive . . .. This latter development accounts for the additional boost of frequency of the bare infinitive that we have noted in formal speech and writing."
  (Geoffrey Leech, Marianne Hundt, Christian Mair, and Nicholas Smith, Change in Contemporary English: A Grammatical Study. Cambridge University Press, 2012)