In Chinese, “刚” and “刚才” have the same meaning, but they have different usages. The following will help you understand how to use the two words.
The similarity between “刚“ and “刚才”
“刚” and “刚才” both indicate that an action or a situation took place not long ago; both can serve as an adverbial modifier.
Your uncle just called and said he sent you an email.
Differences between “刚“ and “刚才”
“刚” and “刚才” have different usages in Chinese. The following will help you understand how to use the two words.
1: I just went to the bathroom.
“刚” is an adverb serving as an adverbial modifier, used only after the subject and before the verb, while “刚才” is a temporal noun that can be used either before or after the subject.
2: Why can't I find the book I borrowed this morning?
“刚” can be preceded by a temporal word, while “刚才” cannot. In the above sentence, in front of the word “刚”, there is the temporal word “上午”, so we should use “刚”.
3: He has only been here for a week.
In the above sentence with “刚”, the verb can be followed by a word of duration, while “刚才” can not. “一个星期” is a word for the duration, others like 一会儿（for a while）, 三个月/天（three months/days), and so on.
4: Why didn't you just say that?
In the above sentence with “刚才”, “刚才” can be followed by a negative word, while “刚” cannot. In Chinese negative words: 不、没.
Practice: Have a try, you are the best!
（1）我 _____ 给我妈妈打了一个电话。
（2）我昨天 _______ 到，有点儿累了，想休息休息。
（3）你 ______ 不在办公室，我把东西给你同事了。
（4）我 _____ 搬来一个星期，对这儿的环境还不太熟悉。