The infinitive is in part a verb, in part a noun. It can be used to express purpose (to, for), and is normally negatived by μη.
The tenses of the active infinitive can be recognised as follows:
Present – λυειν – to set free
Future – λυσειν – to be about to set free
Aorist – λυσαι – to have set free
The use of the perfect tense, which is less common, will be explained later.
It is also helpful to recognise the verb to be – ειναι