たいWant to do

たい is an auxiliary verb that is used to express things that you would like to do (want). To use たい, it needs to be added to the same conjugation base form of a verb that ます would be attached to.

When using たい, the thing that is 'wanted' can either be marked with を, or が. The difference in nuance is that something marked with が is considered to be wanted more. たい is conjugated in the same way as い-Adjectives, meaning that the negative, past, or past-negative forms may also be used.

たい is only used for expressing things that 'you' want, or repeating information/asking questions about what other people want. It may not be used to make guesses about what other people 'may' want, unless asking them directly.

Caution

たい is not used to tell other people that you want them to do something. This is done with ～てほしい.

Caution

たい is not usually used when giving invitations (asking someone if they want to do something with you). In these cases ～ませんか is far more natural.