The speaker's conclusion obtained through deductive, logical judgement or calculation on the basis of what he has heard or read.
Formation
(i) {V / Adj} (i) inf わけ だ {話す・話した}わけ だ (I take it that s.o. talks / talked) {食べる・食べた} わけ だ (I take it that s.o. eats / ate) {高い・高かった}わけ だ (I take it that s.o. is expensive / was expensive)
(ii) Adj (na) stem {な・だった}わけ だ {静かな・静かだった}わけ だ (I take it that s.o. is / was quiet)
(iii) N {という・だった}わけ だ {先生という・先生だった}わけ だ (I take it that s.o. is / was a teacher)