Infinitives and gerunds

There are a few basic rules regarding the use of infinitives and gerunds.

• Infinitives and gerunds are noun forms. If used before the main verb, they are the subject of the verb; after the main verb, they are the object of the verb.
• If a preposition is used after the verb, do not use an infinitive.
• If a common expression ends with a preposition, then it may be followed by a gerund.

Examples:

• Verb + infinitive (A):
  We cannot afford to wait.
• Verb + (pro)noun + infinitive (B):
  That will cause him to think again.
• A or B:
  They are allowed to stay out past midnight.
  Please allow her to be absent tomorrow.
• Verb + gerund:
  I admit getting defensive when I am incorrectly blamed for something.
• Verb + infinitive or gerund:
  You advised me to take that course.
  You advised taking that course.

In addition, some verb phrases take gerunds e.g., carry on (doing something), or put off (doing something). Also, infinitives may be used after a number of adjectives, e.g., happy (to do something) or determined (to do something), or other structures.

For further explanation and more examples of any of this grammar, please consult a grammar reference book.