The word to is frequently used with an infinitive, but it is not an essential part or sign of it. When an infinitive is used without the marker to it is called a bare infinitive.

Uses of the bare infinitive

The infinitive is used without to after certain verbs like bid, let, make, see, hear, need, dare etc.

• I bade him go. (NOT I bade him to go.)
• Let him sit there. (NOT Let him to sit there.)
• She made me cry. (NOT She made me to cry.)
• I heard him sing a lovely song. (NOT I heard him to sing a lovely song.)

The bare infinitive is also used after the verbs will, would, shall, should, may, might, can, could and must.

• I will wait. (NOT I will to wait.)
• You must obey my instructions. (NOT You must to obey my instructions.)
• He can speak five languages. (NOT He can to speak five languages.)
• You should come to school in time. (NOT You should to come to school in time.)

The infinitive is also used without to after had better, would rather, sooner than and rather than.

• You had better ask his permission. (NOT You had better to ask his permission.)
• I would rather die than surrender. (NOT I would rather to die than surrender.)
• He would rather play than work.