1.careless的基本意思指人时是“粗心的”“草率的”,指事物时表示“不用心的”。引申可指“随便的”“自然的”,在句中可用作定语或表语。
2.careless与of连用时表示“不关心的”“淡漠的”,其后多接具体名词。在句中多用作表语。
3.careless表示“做某事不细心”时接“in+v-ing”; 表示“不小心做错了某事”时接动词不定式。

用作定语
▲～+n.
A careless driver is a danger to us all.粗心的司机对我们大家都是一种危险。
A careless mistake cost the company millions of dollars.一次疏忽造成了公司数百万美元的损失。
用作表语
▲S+be+～+prep.-phrase
He used to be careless about his speech.他以前说话常大大咧咧的。
The student was careless about his personal appearance.这个学生不注意个人仪表。
Tom is careless in preparing his lessons.汤姆准备功课不细心。
She is careless about her clothes.她不注重衣着。
▲S+be+～+to-v
Jenny was careless to let out the secret.珍妮不小心泄露了秘密。
▲It is/was+～+of sb+to-v
It was careless of you to leave the door unlocked.你出去时不锁门,太粗心了。

careless about, careless of
这两个短语含义并不相同,前者意为“漫不经心”,后者意为“不在乎”。试比较:
My wife is careless about her clothes.
我妻子对衣着漫不经心。
(对要穿什么衣服漫不经心)
My wife is careless of her clothes.
我妻子对衣着不介意。
(对穿着什么衣服不介意)

careless, carefree
二者均可表示“无忧无虑的”。其区别在于:careless更强调人们从主观上所采取的“无忧无虑”的态度,多用作褒义词; 而carefree则仅从事物的客观状态上描述,多用作贬义词。例如:
On a fine spring day like this,I feel quite carefree.在这样一个春光明媚的日子,我感觉无忧无虑。

他在工作方面非常粗枝大叶。
［误］  He is absolutely careless to his work.
［正］  He is absolutely careless in his work.
［析］  表示“在某方面不仔细”,应该说be careless in...,其中介词in不能换成to。

［同义词］   casual, indifferent, inexact, unmindful, thoughtless, unthinking
［反义词］   careful, cautious, diligent, mindful, tidy, watchful, meticulous