In his book, Did Jesus Exist?, Bart Ehrman argues that Jesus was merely an apolyptic preacher, warning Jewish listeners of the imminent coming of the kingdom of God, to be ushered in "by a cosmic judge whom Jesus called the Son of Man." According to Ehrman, anytime Jesus refers to this future heavenly Son of Man, the saying is authentic. But anytime Jesus refers to himself as the Son of Man, it is an instance of his followers putting words in their leader's mouth, since they thought (though Jesus didn't) that he was the Son of Man. (p.307)
But Ehrman also thinks that Jesus believed that he was the Messiah, who "would be the king of the coming kingdom of God....when the Son of Man brought the kingdom to earth, he, Jesus, would be anointed its ruler." (p.319) So apparently Ehrman thinks that Jesus believed that the Son of Man and the Messiah are to be two different persons.
There seem to be a number of problems with this view. First, is there any evidence that anyone thought the Son of Man and the Messiah were to be two different people? Second, when Jesus refers to the future Son of Man (sayings Ehrman accepts as being authentic), he describes him as a ruler or king (e.g., Matthew 25:31, a saying that Ehrman is quite sure came straight from Jesus's mouth: “When the Son of Man comes in his glory, and all the angels with him, he will sit on his glorious throne"). So who is to be king: Jesus or the Son of Man? Third, earlier in his book, Ehrman pointed out that the Aramaic (Jesus's native language) word for "man" and "son of man" is the same word: barnash. So when Jesus used the phrase "the Son of man" he and his listeners knew that it could also mean "the man." It's difficult to believe that Jesus and his listeners wouldn't wonder why a cosmic judge, who had never been a man, would be called "the Son of man," nor why he would be in a position to judge men. What would make sense is for "the Son of man" to live as a man, a perfect man, who had come to fulfill the Law (which Ehrman thinks Jesus said of himself), and thus earn the right to judge and rule other men. Perhaps Ehrman addresses these issues somewhere else. Unfortunately, just like his forgetting to explain the "author of life" phrase in Acts, he doesn't explain this apparent paradox in this book, either.
Meanwhile, this creates two problems for Ehrman. First, he has argued against the mythicist view by maintaining that the oldest traditions display a Jesus who saw himself as being merely human. Yet he offers us a Jesus who seems to suffer from a split personality. And second, his own view that the oldest traditions are consistent with his view that Jesus was merely human has been severely compromised.
Thanks to Steven Carr, I found out that Ehrman has his own blog. I joined and addressed my concerns to him. If I get an answer, then with his permission, I'll post it on my blog.