Thank you for the question. Most students are taught that the infinitive consists of "to" plus the verb. While we often must use "to" with the infinitive, "to" is not actually part of the infinitive and it is sometimes incorrect to use "to" before the infinitive.
With most verbs sentences follow the format: Subject + verb + to + infinitive.
Examples: I want to eat pizza. Johnny likes to swim. He decided to go to the beach.
The ¨to" in these sentences is REQUIRED: "I want eat pizza" is INCORRECT. "Johnny likes swim" is INCORRECT. "He decided go to the beach" is INCORRECT.
However, many verbs are not followed by "to" before the infinitive. Sentences with these verbs follow the format: Subject + verb + infinitive.
Examples: I heard the band play beautiful music. Ed's boss lets him go home early. Pete's mother makes him wash the dishes.
The use of "to" is not permitted. No, no, no, no, no: "I heard the band to play beautiful music¨is INCORRECT. "Ed's boss lets him to go home early" is INCORRECT. "Pete's mother makes him to wash the dishes" is INCORRECT.
In addition, there is an entire category of verbs called modal verbs or helping verbs with which the marker "to" is also FORBIDDEN: Can: I can dance.
Could: I could run fast when I was young.
May: I may go to Santa Marta on vacation.
Might: It might rain tomorrow.
Must: You must obey the laws of the countries you visit.
Shall: Shall we leave now?
Should: You should drink more water.
Will: I will help you with your paper.
Would: I would eat supper earlier if I didn't work so late.
As always, if you have any questions, feel free to ask them here! And, if you'd like to join our free Wednesday evening live video chat, you would be most welcome. Register for our Business English Video Chat series here.