زيد إنسان؛ لأنه بشر، وكل بشر إنسان
Zayd is human because he is a bashar, and every bashar is human.
In this setting, bashar and insān effectively convey the same human nature. If the question is precisely whether Zayd is human, merely assuming he is bashar, without independently establishing that premise, restates the disputed point.
The issue is not simply that two words are synonyms. The critical question is whether there is independent warrant that Zayd is bashar. Without it, the proof assumes its target.