Shaytan Using Reason
Satan was reasoning but it was invalid because he knows that Allah is his creator he have to obey Allah but due his arrogance he refuse to do it. But point is that even pagans were using reasons for saving their buisness. Ther reason was like “Universe is so big how alone one creator can manage it so he must need some dieties” The differnce between valid and invalid reason is that person himself knows that he is doing it for understanding or just for personal interest.