This link is interesting for its list of options besides the three Lewis presents.
From the link:
The term "trilemma" actually comes from Christian apologist Josh McDowell, who based it on one of Lewis's best-known arguments in favor of Christianity from his book Mere Christianity.
The trilemma argument is as follows:
Most people are willing to accept Jesus Christ as a great moral teacher. However, the Gospels record that Jesus made many claims to divinity, either explicitly ("I and the Father are one") or implicitly, by assuming authority only God had ("The Son of Man has power on earth to forgive sins"). Assuming that the Gospels are accurate, we are thus left with three options.
1. Jesus was telling falsehoods and knew it; so He was a liar.
2. Jesus was telling falsehoods, but believed he was telling the truth; so He was insane.
3. Jesus was telling the truth; so He is divine.
Thus one cannot argue Jesus is only a great moral teacher. If He was a liar or insane, this would invalidate His moral teachings. If He was divine, He is more than just a great moral teacher.
The trilemma argument presumes there are only three options. In logic, dilemmas are countered by proving that it is a false dilemma – that there are more options than the two presented. Skeptics can easily argue that there are several other options available:
1. Jesus's divinity was exaggerated by his disciples.
2. Jesus was misunderstood by His disciples and improperly recorded.
3. Jesus was divine; but as the Hindus point out, there have been many incarnations of God.
4. Jesus was made divine by the developing theology of the Church.
5. Jesus never literally said He was divine; we are misinterpreting those proof-texts.
6. Jesus was a great moral teacher, despite being partly insane.
7. Jesus never existed: the gospels are simply fictions.
Since many of these counter-options deal with the validity of the Gospels, apologists then turn to a defense of Scripture, which Lewis never personally got into. But Lewis's writings indicate that he rejected all the options listed above.
VR: It's simply false to say that Lewis doesn't defend the reliability of Scripture, as I have pointed out earlier.