“This modern slogan seems reasonable at first glance. Many people think knowledge begins and ends with scientific method. Anything else is mere opinion and unsubstantiated belief, a view that is sometimes called “scientism.” However, those who hold this view will be surprised to know that it commits suicide.
Consider this dialog:
“I don’t believe in religion.”
“Why not?”
“There is no scientific evidence for it.”
“Then you shouldn’t believe in science either.”
“Why not?”
“Because there is no scientific evidence for it.”
This was a terse exchange, so let me expand a bit. I noticed first that the slogan “Only science gives reliable truth” is a statement aobut truth that also purports to be true, so it includes itself in what it refers to (in the same way that the statement “All English sentences are false” includes itself). Next, I simply applied our basic test for Suicide by asking, “Can the statement satisfy its own requirement?”
I quickly realized it could not. Since there is no scientific evidence proving that science is the only way to know truth, the view self-destructs. I then used Columbo to point out the flaw.
The next time someone dismisses you with the “Only science gives reliable truth” canard, ask if he wants you to take his statement as a fact or simply as unsubstantiated opinion. If fact, ask what testable scientific evidence led him to his conclusion. As it turns out, this claim is not a fact of science. It is a philosophical assertion about science that itself cannot be proven by the scientific method and would therefore be unreliable, according to this approach.”
(Koukl, Tactics, 118)
Defense of Faith 