が
Particle
1. indicates the subject of a sentence
literary in modern Japanese; usu. written as ヶ in place names
2. indicates possession
Conjunction
3. but, however, (and) yet, though, although, while
4. and
5. used after an introductory remark or explanation
必要, 必用, ひつよう
NA-adjective, 必用 can imply has to be used rather than is just needed
1. necessary, needed, essential, indispensable
2. necessity, need, requirement
歯医者に行く必要はないですよ。
だ
Auxiliary verb, copula, See である, See です, plain copula
be, is
た, だ
Auxiliary verb, だ after certain verb forms; indicates past or completed action
1. did, (have) done
indicates mild imperative
2. (please) do