The texts the argument runs on. Two passages are read as dividing a person into three, and both are short. Paul writes, "may your spirit and soul and body be preserved entire, without blame at the coming of our Lord Jesus Christ" (1 Thessalonians 5:23, ASV). "piercing even to the dividing of soul and spirit, of both joints and marrow, and quick to discern the thoughts and intents of the heart" (Hebrews 4:12, ASV). Against a sharp division stand the texts where the terms overlap freely, Genesis 2:7's "living soul" (ASV), and the command of Deuteronomy 6:5 to love "with all thy heart, and with all thy soul, and with all thy might" (ASV), where the terms accumulate rather than divide.
How the dispute is described by a named source. The 1915 ISBE article "Psychology", also by J. I. Marais, sets it out: "Is man composed of 'body' and 'soul' (dichotomy) only, or is a third to be added to the two, so that 'spirit' is another element in the constitution of human nature (trichotomy)?", and then, in the sentence that matters most for reading it fairly: "Either theory is supposed to be supported by Scripture, and both have had their defenders in all ages of the church." The article records that the three-part reading "found favor in the early church" under Platonic influence and was later "discredited on account of the Apollinarian heresy", naming Apollinaris of Laodicea (died 382).
🚨 That source argues for one side, and saying so is part of quoting it. Marais does not stop at describing the dispute; he takes the two-part view, writing of 1 Thessalonians 5:23 that "There is evidently no distinction of essence here" and of Hebrews 4:12 that "to found a doctrine of Trichotomy on an isolated, variously interpreted text is dangerous in the extreme." He is a named 1915 witness with a position, not a neutral referee, and his summary of the opposing case is a summary written by someone who rejects it. The three-part reading has been held throughout church history on the plain wording of 1 Thessalonians 5:23 and the distinction drawn in Hebrews 4:12, and it is not answered here.
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What the words themselves settle, and what they do not. The lexicons settle that nephesh and psyche correspond, that ruach and pneuma correspond, and that the Hebrew terms overlap heavily in ordinary use, Abbott-Smith's own synonym note offers a distinction between psyche and pneuma and offers it as one dictionary's formulation.
They do not settle how many parts a person has. That question is answered from whole texts and theological reasoning, both sides have held it in every century, and this file names the positions and stops.
Sources: 1 Thessalonians 5:23; Hebrews 4:12; Genesis 2:7; Deuteronomy 6:5; ISBE 1915, "Psychology" (J. I. Marais), sections 5 and 6; TBESG entries G5590G and G4151G (Abbott-Smith synonym notes).
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