The Bible teaches that humanity possesses a physical body, a soul, and a spirit. In regards to how these aspects of the human nature connect with and relate to each other, there are four primary theories. Two of the views, anthropological monism and anthropological hylomorphism, deal primarily with how the three aspects of humanity combine to form the human nature. The two other models, dichotomy (anthropological dualism) and trichotomy, deal with the distinction between the human soul and human spirit. The distinction between the material (physical) and immaterial (spiritual) aspects of the human nature is straightforward. The distinction between the two immaterial aspects of the human nature is more difficult.
While there are Bible verses which use the terms soul and spirit interchangeably (Matthew 10:28; Luke 1:46–47; Acts 2:31; 1 Corinthians 5:3; 6:20; 7:34; 2 Peter 2:11), other biblical passages do not present the soul and the spirit as precisely the same thing. There are also passages which hint at the separation between the soul and spirit (Romans 8:16; 1 Thessalonians 5:23; Hebrews 4:12). Hebrews 4:12 states, “For the word of God is alive and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit …” This verse tells us two things: (1) there is a dividing point between the soul and spirit, and (2) the dividing point is only discernible to God. With all of these verses in mind, neither the dichotomous or trichotomous interpretations can be explicitly proved. Does the immaterial aspect of the human nature involve a soul and a spirit? Yes. Are the soul and spirit absolutely unified and united (dichotomy) or closely-related but separate (trichotomy)? Unclear.
Those who believe that human nature is a trichotomy typically believe the following: the physical body is what connects us with the physical world around us, the soul is the essence of our being, and the spirit is what connects us with God. This is why the unsaved can be said to be spiritually dead (Ephesians 2:1; Colossians 2:13), while they are very much physically and “soulishly” alive. Those who believe that human nature is a dichotomy would have the same understanding of the body, but would view the spirit as the part of the soul that connects with God. So, the question of dichotomy vs. trichotomy is essentially whether the soul and spirit are different aspects of the immaterial human nature, or if the spirit is simply a part of the soul, with the soul being the whole immaterial part of the human nature.
Trichotomy vs. dichotomy of man—which view is correct? It would seem that it is unwise to be dogmatic. Both theories are biblically plausible. Neither interpretation is heretical. This is perhaps an issue we are unable to fully grasp with our finite human minds. What we can be certain of is that the human nature is comprised of a body, a soul, and a spirit. Whether the soul and spirit are one, or are somehow distinct, is not an issue God chose to make abundantly clear in His Word. Whether you believe in a dichotomy or trichotomy, offer your body as a living sacrifice (Romans 12:1), thank God for saving your soul (1 Peter 1:9), and worship God in spirit and truth (John 4:23–24).
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.