b[経験][頻度を示す語句を伴って] …したことになるだろう‖I shall have taken the examination three times if I take it again. もう一度試験を受けると3回受けたことになる.

c[継続][期間を示す語句を伴って] …していることになるだろう‖By the end of next month she will have been in (the) hospital for six months. 来月末で彼女は半年入院していることになる.

[語法] (1)can, may, must, need などの助動詞の後で用いる完了形は「過去」「現在完了」を表す： She cannot have done such a thing. 彼女がそんなことをしたはずがない(＝I'm sure that she didn't do [hasn't done] such a thing.). (2)不定詞・分詞・動名詞の完了形は主節の動詞の示す時よりも前の時を表す： He seems to have been ill. 彼は病気だったらしい(＝It seems that he has been [was] ill.) / Having finished my work, I went out for a walk. 仕事をすましたあと散歩に出かけた(＝After [When] I had finished my work, I went out for a walk.). (3)次の場合は未来完了形を用いて, 現在から見た過去の推量を表す：You'll have already received my letter. もうすでに私の手紙を受け取られたと思います(＝I suppose you have already received my letter.). この will は「未来」ではなく「推量」を表す( →will^１ 【助】 II4b). (4)未来完了形はやや固い感じがするので((略式))では次のような表現をすることが多い：We'll be through with the repairs by Friday. / We'll have the repairs finished by Friday. 修理は金曜日までに終っているでしょう(＝We'll have finished the repairs by Friday.). (5)((略式))では未来完了形の代りに未来時制を使うことも多い：I'll finish my homework by tomorrow. 明日までに宿題を終えられるだろう.