Single word Sentences

Question 1

In Japanese single words can be sentences, more specifically, single verbs.

So long as you are saying it with context involved.

For example…

Answer 1

By saying ‘うたい’ + ‘ます’ (sing will)

or ‘うたい’ + ‘ません’ (sing not)

You are making a perfectly logical statement by saying you will sing or will not sing.

This only makes sense in context though, so in this case, someone probably asked you if you are going to sing.

If you did this in English it would sound weird but in Japanese, this is very common and grammatically correct.