Both ἀγράμματος and ἰδιώτης are translated 'unlearned,' but there is a difference between them. Both words occur in Acts 4:13; the rulers of Israel perceived Peter and John to be "unlearned (ἀγ.) and ignorant (ἰδ.) men. ἀγράμματος(from a neg. and γράμμα, 'a letter') occurs nowhere else in the N.T., but γράμμαoccurs in John 7:15 : "how knoweth this man 'letters'?" and in Acts 26:24; "much 'learning' doth make thee mad." These instances show that ἀγράμματοςsignifies 'unlettered.'
ἰδιώτης (from ἴδιος, 'one's own') has a different signification: it is applied to private persons in distinction from those who are officials or professionals, and so to simple or uninstructed persons. The apostle asks how such a one could say Amen to the giving of thanks by one speaking in a tongue, not understanding what was said, 1 Corinthians 14:16; and in 1 Corinthians 14:23,24 he is classed with unbelievers. The word occurs also in 2 Corinthians 11:6 , where Paul maintains that though he may be simple, or untrained, in speech, he is not so in regard to knowledge.