To INFINITIVE

1. We use the to-infinitive

1.1. To express purpose (to answer "Why...?")

1.1.1. We sometimes say in order to or in order not to

1.1.1.1. We set off early in order to avoid the traffic. They spoke quietly in order not to wake the children

1.1.2. … or we can say so as to or so as not to

1.1.2.1. We set off early so as to avoid the traffic. They spoke quietly so as not to wake the children.

1.2. after certain verbs (see verbs followed by infinitive), particularly verbs of thinking and feeling

1.2.1. choose, decide, expect, forget, hate, hope, intend, learn, like, love, mean, plan, prefer, remember, want, would like, would love

1.2.2. … and verbs of saying

1.2.2.1. agree, promise, refuse

1.2.3. Some verbs are followed by a direct object and the infinitive(see verbs followed by infinitive)

1.2.3.1. advise, ask, encourage, invite, order, persuade, remind, tell, warn, expect, intend, would prefer, want, would like

2. As a postmodifier (see noun phrases) after abstract nouns like

2.1. difficult easy possible impossible hard right wrong kind nice clever silly foolish

3. We often use the to-infinitive with these adjectives after it to give opinions