情况的变化（1） Changed circumstances (1)

The particle “了” is employed at the end of a sentence to indicate changed circumstances or the emergence of some new situation or status. This usage of “了”frequently occurs in sentences with adjectival predicates, or sentences with “是”or “有”as the verb. For example:
你舅舅也老。 （以前不老）
现在天气冷了。（以前不冷）
雪大了。（以前不大）
你是大学生了。（以前不是）
我有男朋友了。（以前没有）

In sentences with verbal predicates, the particle “了” often emphatically confirms the completion or realization of some event or situation (refer to Lesson 15), sometimes it can also indicate changed circumstances. For example:
现在他当蔬菜公司的经历了。（以前没当）
你舅妈也开始用电脑了。（以前没用）
（她）上大学二年级了，（以前没上）

Also, in sentences with the negative adverb“不”preceding a verbal predicate, the preceding a verbal predicate, the particle “了” at the end of the sentence often indicates a change. Foe example:
她这次不来了。（以前打算来）
他不认识我。（以前认识）