Preface: You can read all below, but in retrospect I wasn't very clear.
Highly recommend instead starting with Plantinga's own description of the argument here:
This is part 1 of a 6 parts series (about an hour combined together).
Once you get the gist of the argument, then what I say below ought to make greater sense where I really do perhaps just jump right in.
Alvin Plantinga has made this one of his personal arguments.
When appropriately framed, this is one main reason I believe one must necessarily be Theist if they're to rationally accept the ToE as true.
According to Theism, we human beings and all Creation have been created by a wholly good, all-knowing Being (i.e., God).
Furthermore, in Theistic belief systems like Judaism and Christianity it is said that we are created in God's image.
A part of that image, involves, the reliability of cognitive faculties and ability to know things about ourselves and the world, as Thomas Aquinas says:
"Since human beings are said to be in the image of God including a human nature involving an intellect."
And so, only in rational creatures, creatures with reason, is there found a likeness of God.
So what are our cognitive faculties there for?
Most of us would think that at least one function of our cognitive faculties is to provide us with true beliefs.
And when they're functioning properly, when there's no malfunctioning, and for the most part that's what they do.
Now contrast the Theistic grounding for reliable cognitive faculties against Naturalism.
Naturalism says all of what we see exists only minus God out of the picture.
Some popular Naturalists would be Carl Sagan ("the cosmos is all there is, or ever has been, or ever will be"), Stephen J Gould, David Armstrong, Darwin (later in life), Bertrand Russel, Richard Dawkins, Daniel Dannet and the like.
Isn't there a problem here for the Naturalist?
That is, the Naturalist who believes that we and our cognitive faculties have arrived on the scene by Evolution.
After some billions years of evolution, by the way of natural selection, genetic drift and other blind processes working on sources of genetic variation like random genetic mutation.
Isn't there a problem? If this is the way we should think of it, then shouldn't we be surprised that our rational faculties are in fact reliable?
If Naturalism and Evolution are both true, it seems greatly improbable that our cognitive faculties (memories, reasoning, etc) would in fact result in true beliefs.
Given this, if you believe in both Naturalism and Evolution, then you have a defeater for believing your cognitive faculties are reliable.
But, we can hardly deny what seems intuitive to us -- that is, our cognitive faculties do provide us with true information about the world.
We can no further deny this then we could unflinchingly cut off our own arm (now perhaps some wierdo could do that, but you get what I mean).
So it turns out that we have a defeater for belief in both "Naturalism" and "Evolution" together. One of these must be dropped.
And if Evolution is beyond scientific doubt, we must then drop Naturalism.
Dawkins has stated that Darwin made it possible to be an intellectually fulfilled Atheist.
It is rather ironic that it seems to be more the case that Darwin's theory actually makes it irrational to be an Atheist.
How the words of the Agnostic Robert Jastrow seem to ring true:
- For the scientist who has lived by faith in the power of reason, the story ends like a bad dream. He has scaled the mountains of ignorance; he is about to conquer the highest peak; as he pulls himself over the final rock, he is greeted by a band of theologians who have been sitting there for centuries.