当然だ/当たり前だ => natural; as a matter of course N2
て/なくて => Because/Because not N4
なくして(は)~ない => cannot do without ~ N1
なければならない/なくてはならない/なければいけない/なくてはいけない/なければだめ/なくてはだめ => must N5
なくては => If not... then no... N3
Conditions (necessary conditions)
て も~なくても => even if not,even without N4
Invariant
ではなくて => Not A but B N4
Emphasize the negative meaning
~でなくてなんだろう => must be; is definitely ~ N1
Emphasize
なくてはいけない => must do; need to do N3
Conditions (necessary conditions)
なくて済む/ないで済む => get by without doing ~ N2
昼となく夜となく => day and night N1
Continuous
くて => Adjective and adjective N5
List