The one who is deceived is the insane, because he has been tested: that is, he is afflicted with insanity. Or because the Arabs claim that it is due to the madness caused by the jinn, and they are the deceivers among the fierce ones. The 'b' is an addition. Or 'the deceived' is a noun like 'the rational' and 'the beaten,' meaning: in which of you is the insanity? Or in which of the two groups among you is the insanity? Is it among the believers or among the disbelievers? That is, in which of them is there one who deserves this name: and this is an allusion to Abu Jahl ibn Hisham and Al-Walid ibn Al-Mughira and their likes. This is like His saying, 'They will know tomorrow who is the lying, arrogant one.'