|Aside from the basic form of infinitives (to+base verb), they also come in progressive, perfect, and passive forms.|
|1. Progressive/Continuous Infinitive|
|Form: (to) be + -ing|
|Meaning: As it's name suggests, the progressive or continuous infinitive expresses an action or event in progress or happening at the time of speaking.|
You must be joking.
I'll be heading to New York around this time next month.
At that time, Keshia was confirmed to be staying with her aunt.
|2. Perfect Infinitive|
|Form: (to) have + past participle|
|Meaning: The perfect infinitive refers to a time in the past before that of the preceding verb.|
I'm glad to have worked at that company.
Paul must have forgotten about the deadline.
Nick was assumed to have checked out the day before.
|3. Passive Infinitive|
|Form: (to) be + past participle|
|Meaning: Functions similarly to other passive forms. When used after a noun or be, active and passive connote the same meaning.|
This meat has to be cooked.
These gates should be shut always.
I am expecting to be offered a promotion.
|Perfect progressive + perfect passive infinitives are usual.|
You must have been tired working all night.
Jimmy would like to have presented the flowers to the queen.
|Progressive/Continuous passive infinitives though acceptable are uncommon.|
He'd like to be being cheered on every time.
Mr. Yoshi like to be being seated near the window.
|Progressive/Continuous perfect passive infinitives are very rare.|
The tower must have been being put up without any machinery.
Bianca must have been being scolded at that time.
|5. Negative Forms|
|Form: not + infinitive|
|Meaning: To form the negative infinitive, place not before the to- or zero infinitive.|
He asked me not to be late.
Elephants ought not to marry mice.
You'd better not smile at the crocodile.
|6. To form|
|a. Used before an infinitive|
Form: to + infinitive
Example: He wanted to sleep.
|b. Without to|
Example: Nancy let Clark answer the phone.
|7. Split infinitive|
|Form: to + adverb + infinitive|
|Meaning: To form split infinitives, separate "to" and infinitive by inserting adverb between them.|
He tried to really prove his point.
Jack hopes to easily excel in class.