Most Christians agree that humans have both a material and an immaterial nature; however, throughout history there has been much discussion about whether humans are threefold beings or twofold beings. The technical terms for these two views is trichotomy and dichotomy. These are the traditional views that Christians believe have biblical support.
The first view to examine is the trichotomist view. The word trichotomy is derived from two greek words: τρίχα (tricha) meaning, “in three parts” and τέμνειν (temnein) meaning, “to cut.” Therefore, trichotomy signifies a division of three parts, and so from a trichotomy view, humans are composed of three elements: body, soul and spirit. The greek word often used for the material part of humans is σῶμα (sōma) meaning, “body.” This physical σῶμα (sōma) is similar to the makeup of animals and plants. Millard Erickson writes, there is no difference in kind between a human body and that of animals and plants; but there is a difference of degree, as humans have a more complex physical structure.”
As for the immaterial elements of humans, the greek words ψυχή (psuché) meaning, “soul” and πνεῦμα (pneuma) meaning “spirit” are used in distinguishing ways from the trichotomist perspective. The ψυχή (psuché) “soul” is viewed as the element that enables human consciousness with the faculties of “reason, emotion, social interrelatedness, and the like.” The πνεῦμα (pneuma) “spirit” is viewed as the religious component of humans enabling them to experience spiritual things. Proponents of the Trichotomy perspective point to biblical passages such as 1 Thess 5:23, Heb 4:12, 1 Cor 2:14 -3:4.
Next, we examine the dichotomist view. The term dichotomy is derived from the greek words δίχα (dicha) meaning, “in two parts” and τέμνειν (temnein) meaning, “to cut.” Thus, dichotomy signifies a twofold division of humans. From the dichotomy perspective, humans are composed of the two elements: σῶμα (sōma) “body” and ψυχή (psuché) “soul.” Similar to the trichotomy perspective, the dichotomy perspective posits that the σῶμα (sōma) is the physical part of humans that is in common with animals and plants. It is the part that dies and returns to the ground. In the dichotomy perspective, the ψυχή (psuché) is the rational, immaterial and immortal part of humans, and this is the part that differentiates humans from other creatures. Proponents of the dichotomy perspective support their position by pointing to biblical passages such as Matt 6:25, 10:28, Ecc 12:7 and 1 Cor 5:3-5.
Moreover, proponents of the dichotomy perspective object to the trichotomy proponents who differentiate between “soul” and “spirit.” They argue that there are many examples in Scripture where “soul” and “spirit” are used interchangeably or as synonyms (ex. Luke 1:46-47; also, Gen 41:8, Psa 42:6, Matt 27:50, Heb 12:23 and Rev 6:9).
An Alternative Model: Conditional Unity
Some have argued that the full range of Scripture presents humans as an embodied unitary being or as a conditional unity. This is the idea that humans in their normal state are a material and immaterial oneness, but this unity is temporarily dissolvable at death. However, at the eschatological resurrection the immaterial will once again become inseparable with a new, perfected resurrected body. The implications of the conditional unity perspective are that humans are to be treated as unified and complex beings who can not be reduced to one aspect or principle. This means that all aspects of human nature must be attended to and respected. Moreover, God is at work in renewing the whole person, and so spiritually speaking one part of human nature should not be subjugate to another.
 W.E. Ward, “Trichotomy” in Evangelical Dictionary of Theology (EDT), edited by Daniel J. Treier and Walter A. Elwell, 3rd. ed. Grand Rapids, MI: Baker Academic, 2017.  Millard Erickson, Christian Theology 3rd ed. (Grand Rapids, MI: Baker Books, 2013), 477.  Erickson, Christian, 477.  Erickson, Christian, 477.  W.E. Ward, “Dichotomy” in EDT, EPUB edition.  Erickson, Christian, 478.  Erickson, Christian, 491-493.