-u: commands, let us, and asking politely

-u: the command

The Fundamento calls -u the imperative (ordona modo). Many later grammars call it the volitive (from voli, to want), because it marks any action somebody wants to happen, not only an order. The plain command is the commonest case:

There is no do to add in a negative command: ne goes in front and that is all. The bare form is the neutral command; stating vi points a finger.

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1. 1Sidiĝu!
2. 2Malfermu la libron!
3. 3Ne kuru!
4. 4Silentu!

Sidiĝu! Sit down! Malfermu la libron! Open the book! Ne kuru! Do not run! Silentu! Be quiet! Every one is the root plus -u.

Ni iru, li venu, kion mi faru?

-u works with every person, which gives Esperanto one form for what English does with let, should and shall:

Kion mi faru? asks what you are wanted to do. Kion mi devas fari? (what must I do?) is also correct, but it asks what is obligatory, which is a slightly different question.

From blunt to polite

A request can be a bare command, a bonvolu, or a polite -us question. The strip runs from blunt to soft:

Bonvolu is itself a -u form: bonvoli is to be so kind as to, and the infinitive follows it. Mi volas paroli kun vi is not rude, but it lands like I want a word; mi volus is I'd like a word.