疑う; ~ではないだろうと思う (suspect)
I doubted my eyes.
I doubted my eyes.
(これが本当かと)私は自分の目を疑った.
I doubt if [whether] he will keep his word.
I doubt if [whether] he will keep his word.
私は彼が約束を守るかどうか疑問に思う.
I doubt (that) he will come.
I doubt (that) he will come.
彼が来ることなんかありえないと思う[きっと来ないと思う].
⦣ 非常に強い疑いの気持ちを表す.
I don't doubt (that) he will keep his word.
I don't doubt (that) he will keep his word.
私は彼が約束を守ることを疑わない.