Unaccusative verbs have a single argument (typically a theme or experiencer) that can occupy either the object or the subject position.
来了一位朋友。
lai2 le0 yi1 wei4 peng2you3
come LE one CL friend
‘Here came a friend.’
朋友们来了。
peng2you3men2 lai2 le0
friends come LE
‘The friends came.’
Reference
Li, Y.-H. Audrey. 2016. Verbs and verb phrases. In A Reference Grammar of Chinese, eds. by Chu-Ren Huang and Dingxu Shi. Cambridge University Press.
