A.T. Robertson Commentary James 1:8

"a doubleminded man, unstable in all his ways." — James 1:8 (ASV)

Man (ανηρ). Instead of ανθρωπος (general term) in verse 7, perhaps for variety (Ropes), but often in James (1:12,23; 2:2; 3:2), though in other Epistles usually in distinction from γυνη (woman).

Double-minded (διψυχος). First appearance of this compound known and in N.T. only here and 4:8. Apparently coined by James, but copied often in early Christian writings and so an argument for the early date of James' Epistle (Moulton and Milligan's Vocabulary). From δις twice and ψυχη soul, double-souled, double-minded, Bunyan's "Mr. Facing-bothways." Cf. the rebuke to Peter (εδιστασας) in Mt 14:31.

Unstable (ακαταστατος). Late double compound (alpha privative and καταστατος verbal from καθιστημ), in LXX once (Isaiah 54:11) and in Polybius, in N.T. only here and 3:8. It means unsteady, fickle, staggering, reeling like a drunken man. Surely to James such "doubt" is no mark of intellectuality.