English verbs have 3 moods – imperative, indicative, and subjunctive/conditional, linked to sentence types.
The indicative mood expresses activity as a fact in declarative (affirmative/negative) and interrogative (affirmative/negative) sentences. It’s the main mood, describing reality and make inquiries with finite verb forms. Most statements are in the indicative.
I know you write such things in your notebook.
The imperative mood expresses activity as an urge (command, prohibition, request, advice) in imperative and exclamatory sentences. It’s the simplest mood, with 2 forms – active (simple infinitive) / passive (passive infinitive). Passive imperatives are very rare.
Write it in your notebook.
Imperatives may sometimes be emphatic with the preceding helping do.
Do wake up!
Negative imperatives are very common as starting with don’t.
Don’t give up.
Negative imperatives may sometimes be emphatic with the preceding you. Such informal imperatives shouldn’t be confused with declarative sentences, in which context and the exclamation mark usually help.
You don’t say no!
Nominal affirmative imperatives have become so formal that now they are obsolete.
God bless America!
Another imperative turn is with the verb let meaning suggestion for implied you. The most common form is let’s.
Let it be.
The conditional mood expresses activity as problematic/unreal in declarative (affirmative/negative) and interrogative (affirmative/negative) sentences. It’s the most troublesome mood with many types, factors and meanings.
I wish you wrote such things in your notebook.
The conditional expresses indirect advice and requests in purpose clauses after the verbs advise, ask, command, demand, insist, order, recommend, request, require, suggest, urge.
The teacher asked that we be quiet.
For hypothetical future we use Present Simple as a condition ((as) if) and Future Simple as an outcome.
If I (should) see him, I’ll tell him.
For unreal present (wishes) we use Past Simple in conditional clauses and often the subjunctive modals should/would/could/might in main clauses. Conditional be becomes were (nor was).
If I were you, I wouldn’t keep driving on those tires.
I wish you were here.
For unreal past (suppositions) we use Past Perfect in clauses and often subjunctive modals with perfect infinitives in main clauses.
If I had told you the truth, you’d have fainted.
Wish is also formally expressed by the verb may.
May you live long and prosper.