Trinitarians claim that since Jesus is the son of man it means he is a man and we should consistently reason that is he is a son of God then he is God.
Examination of the Claim
1. Logical Fallacy
Trinitarians are here committing a categorical fallacy by confusing definitions of the terms. In short they are comparing apples and oranges. To argue that the term "son of man" means Jesus is a man is to imply the term "man" refers to human nature. This definition of "son of man" is being suggestively used to mean "son of humanity" or "son of human nature" in contrast to "son of divine nature." However, we can see clearly in the Scriptures the term "son of God" is to used to refer to the son of another person, not the son of a nature. It is a term which means that Jesus is the son of another identity, namely, God the Father.
The error in this claim is easily seen when we ask the Trinitarian that if Jesus is a son of Adam does that mean he is therefore "Adam" by identity? No, it does not. In the same way, if Jesus is a son of God it does not mean he is the one God by identity.
The term "son of man" means that a person is the son of a man and ultimately a son of the first man Adam. In Hebrew it is "ben Adam", a son of Adam, the son of an identity. In the same way, the term "son of God" means that one identity is the son of another identity. Jesus is the "son of the Father" (2 John 1:3).
Also hidden within the Trinitarian claim here is a false premise. The premise is that if you have the divine nature of God then you are God. But it is plainly evident that we have the human nature of Adam and we are not Adam. The most anyone can say is that having the divine nature of God the Father means you are divine just as having the human nature of Adam our Father means we are human. But just as being human does not make anyone the one person Adam by identity, being divine does not make anyone the one God by identity.
2. The One God is not a Son of Man
God is not a man, that He should lie, Nor a son of man, that He should repent. (Numbers 23:19).
3. The Israelites are Sons of God
You are the sons of the LORD your God. (Deuteronomy 14:1; cf. Ex. 4:22; Deut 32:6, 18-19; Psalm 29:1; Rom 9:4).
4. The Judges of Israel are Sons of God
I said, "You are gods,and sons of the Most High - all of you. Nevertheless you will die like men and fall like any one of the princes."
5. Angels are Sons of God
Where were you when I laid the foundation of the earth?.... When the morning stars sang together and all the sons of God shouted for joy? (Job 38:4,7).
6. Satan is a son of God
Now there was a day when the sons of God came to present themselves before the LORD, and Satan also came among them. (Job 1:6).
7. Christians are Sons of God
You are all sons of God through faith in Christ Jesus. (Galatians 3:26).
The Trinitarian error is also made plain when we recognize that true disciples of Jesus are sons of God. In fact, just as Jesus was begotten from above by the Spirit of God, all the disciples of Jesus are begotten from above by the Spirit of God. For this reason Jesus is described as the "firstborn of many brothers." God is the true Father of the disciples and indeed they are all "partakers of the divine nature" and Jesus also teaches they "will be like the angels being sons of the resurrection." And of course it does not mean any of them are "God." The very same thing is true of Jesus. Trinitarians need to stop confusing or conflating identity and nature and accusing everyone else of the very error they commit themselves.
It is quite easy to see that "son of man" does not make one Adam and "son of God" does not make one "God." Angels are also sons of God yet Trinitarians do not try to claim that this means they are the one God. And being one of those angels, Satan is also a "son of God." Moreover, believers in Jesus are "sons of God." The term means one is a son of another identity called "God."
Last Updated: June 15, 2011 (minor edits)