1. 注意以下句型：
你把钱包放在这里真是太大意了。
正：It was careless of you to leave your wallet here.
正：You were careless to leave your wallet here.
以上第一句句首的 it 为形式主语，不能改为 that。但是若以上句型后面不出现不定式，那么句首的 it 也可换为 that。如：
他太粗心了。
正:It was very careless of him.
正:That’s very careless of him.
2. 比较：
正：He was careless to make the mistake. 他很粗心，结果出 了错。(句中的不定式为结果状语)
正：He was so careless as to make the mistake. (同上)
正：He was careless in typing the letter. 他打这封信时很 粗心。(句中的 in typing the letter有类似 when he was typing the letter 的意思)
误：He was careless to type the letter. (若此句视为正句，则只能理解为：他很粗心，结果把那封信打印了出来)
3. 表示“不在意的”、“不关心的”等，其后可接介词 about, of, with 等。如：
He’s careless of [about] his speech. 他讲话随便。
She is careless of [with] his health. 她不注意身体。
He is careless with his pronunciation. 他对语音不注意。
Don’t be so careless with your money. 你花钱不要这样随便。