Son of man is a typical Semitic expression (‘son of …’= one of the species of) denoting an individual human being (Ps. 8.4; Job 16.21). Paradoxically it comes to refer, in Jewish texts, to a heavenly figure who looks like a human being and, in New Testament texts, to Jesus both in his humanity and in his identity as the heavenly figure described in the Jewish texts.
The earliest relevant text for the non-generic use of ‘son of man’ is Dan. 7.13–14. The chapter purports to be a vision that Daniel…