Page 539 - Basic Japanese

Colloquial words, lively particles like yo and ne, and
ii.
contractions like ja for de wa and n for no are avoided.

iii. The copula da is replaced by the phrase de aru or de
arimasu. The phrase is inflected just like aru:

Imperfect = da = desu
de [na, de arimasu

aru no]

Perfect = = deshita
de datta de

atta arimashita

Tentative = darō = deshō
dearō de arimashō

Gerund = de = deshite
de de

atte arimashite

Infinitive = ni,
de ari de

Provisional = nara
de

areba

Conditional = =
de dattara de deshitara

attara arimashitara