What is the infinitive and how is it used in English?

The infinitive is the so-called base form of the verb, which is unconjugated and so ‘unchanged’. It is typically indicated with ‘to’ in the English language. It is also the form that is displayed in a dictionary when looking for a verb. However, when used in a sentence, it may appear without ‘to’ as well. The following uses are possible:

• For English verbs, the infinitive (base form) is signalled with ‘to’, which stands immediately before it in most of the cases (for exceptions to this practice, have a look at split infinitive). Some examples of infinitives are:
  • to go, to do, to drink, to hear, to realize, to fly, to exercise, to write, to watch, to break, etc.
• In a sentence, the base form appears with ‘to’ (and for this reason, as the to-infinitive) in the following cases:
  • After adjectives, which may also be compared:
    • “It’s nice to see you.”
      • with ‘nice’ in its positive form
    • “It is sometimes harder to walk quickly than to jog at a comfortable pace.”
      • here with the adjective ‘harder’ in its comparative form
    • “Sandra is too tired to go out.”
      • This statement includes the adjective ‘tired’ that is modified by the intensifier ‘too’ and followed by the to-infinitive ‘to go’.
  • After question words (‘when, why, how, who’, etc.):
    • “As a boy scout, I learned how to make a fire.”
    • “I don’t know what to say.”
  • After certain verbs (‘want, agree, forget, promise, use’, etc.) that require the infinitive:
    • “Marc promised me to pick me up.”
    • “My sister wants to ask you something.”
  • After the expressions ‘the first, the last’, and ‘the next’:
    • “Maya was the first to receive her test result.”
    • “The captain was the last to leave the sinking ship.”
• The infinitive can also be used without ‘to’. Then, it is called the bare infinitive and occurs primarily in sentences such as these:
  • After the auxiliary verb ‘to do’:
    • “Peter doesn’t play tennis.”
    • “I don’t like fish very much.”
  • After modal verbs (‘can, will, could, might, must, should’, etc.):
    • “My father can cook very well.”
    • “You mustn’t smoke in here.”
  • After certain fixed expressions like ‘Why not …’ or ‘… had better …’:
    • “Why not go to the cinema tonight?”
    • “I had better go to work now, or my boss will get angry.”

What are the additional infinitive forms?

In addition to the verb forms mentioned above, two further forms exist: the continuous infinitive and the perfect infinitive. These two are used as follows:

• Both base forms are common with the following verbs:
  • appear
  • claim
  • pretend
  • seem
  • tend

Rule for forming the continuous infinitive

The progressive or continuous infinitive needs the auxiliary ‘to be’ and the ing-form of the verb:

‘to be’ + ‘verb-ing’ (present participle)

Examples of using the continuous infinitive

• “When he looked at her, she was pretending to be talking on the phone.”
• “My colleague appears to be having a discussion with his boss.”

Rule for forming the perfect infinitive

The infinitive in the perfect aspect is created by using ‘to have’ and the past participle of the corresponding verb. Compare:

‘to have’ + past participle

Examples of using the perfect infinitive

• “Peter claimed to have done his homework.”
• “He seems to have had a bad day.”

Further explanations relating to the ‘Infinitive’

The following explanations relate to the topic ‘Using the infinitive of the verb in English grammar’ and could therefore be helpful too:

• Use of auxiliary verbs in English
• Main (lexical) verbs in English
• Use of the gerund in English
• Use of the infinitive without ‘to’
• List of exercises about parts of speech