(the third-person plural nominative) A group of entities previously mentioned.

(now Southern England dialect or nonstandard) The, those. / (US dialects, including African-American Vernacular) Their.

(US dialectal) There (especially as an expletive subject of be).

they have

Contraction of they are.

Misspelling of there.

Misspelling of their.

They had. / They would.

Contraction of they will. / Contraction of they shall.

One should not depend upon a favorable (and typically overoptimistic) outcome to one's plans until it is certain to occur.