This is definitely a pretty good primer, though it seems to have a few significant flaws here and there, particularly in part 8 where he appears to misunderstand modern science enough to disagree with the likes of Dawkins, Harris, Pinker, and Hawking. The modern methods of scientific inquiry, making great use of statistical analysis and in particular bayes theorem, has progressed quite a ways beyond Popper's falsificationism. He also apparently has a very narrow view of science if he thinks that things like psychedelic experiences fall outside the realm of science.
He also states, as an argument that there are things outside of science that we can know: "But again: What if something can’t (yet) be counted, measured, weighed, or tested? Does that mean it’s not real or true, or that it doesn’t exist, or didn’t happen? Of course not."
He softens his position with the parenthetical "yet" which makes this all a list of things that merely lies outside of the realm of our current technology and in no way an argument about the validity of unscientific knowledge. If you make the stronger claim (the one without the "yet") then I would argue that, yes, this does mean that the thing you're talking about doesn't exist or didn't happen. In what way can we coherently talk about something's existing or happening if it cannot, even in principle, impact our experience in some way (the essence of what 'measuring, weighing, or testing' is)? You might argue that concepts such as extra spacial dimensions (suggested by string theory or super gravity) or parallel universes (Everett interpretation of quantum mechanics, eternal inflation theory) fit into this category, but they do not - if true their existence impacts our lives by allowing or disallowing certain configurations that our universe can take, and while we may not (yet) be able to state them as fact with the same level of certainty that we give to the laws of thermodynamics or to evolution, etc, they are still suggested by the actual physical facts of the universe.
He goes on to list examples of things that he claims are true but outside of science. They are: Mathematical Truths, Metaphysical Truths, Ethical beliefs (interesting that he decides at this point to stop using the word truth, leaving it only to be implied by the inclusion in the list), Aesthetic judgements,and science itself.
Math is used because it works. That sounds like the scientific method to me - we set up a system of rules, tested it against reality, and time and again it works. The examples of metaphysical truths he names (existence of other minds, the realness of the external world, and the refutation of last thursdayism) are also suggested by occam's razor which is the basis of science (it usually takes the form of the null hypothesis), furthermore none of these facts can be said to be "true" with the same kind of certainty as mathematical truths - he's now started making the fallacy of false equivocation. He's used the word "truth" (and implies it's usage later in the list) in different and incompatible ways. Metaphysical "truths" are not similar to mathematical "truths." Next, in the case of ethics and aesthetics, he gets to much shakier ground - these things are not true in any objective sense because they rest upon implicit assumptions in the mind of the one making the judgement. As soon as you make those assumptions explicitly specified what happens? Science tells you what's best. Then, in an appeal to the problem of infinite regress, he mentions science itself. But we use science because it works. See the point made about math.
He's correct that the term science/scientific gets thrown around by people on occasion to give false ideas greater weight, but that's a misuse of the term, not a problem with science itself. In any of the examples he gave of things that we "know" to be true but are outside the realm of science, it's either because of hidden axioms that, made explicit, enter the topic into the realm of science or it's because he's asserting something as true when it really isn't.
Reading some of his other stuff, I think I've found his motivation for wanting to believe things can be true but unscientific - he's a big believer in the usefulness of psychedelics (I'm a fan myself, so I don't say this as an ad-hominem) but instead of acknowledging that the psychedelic experience merely tells us more about what other possible conscious states might exist and that our minds are capable of producing a vast range of experience, he seems to want to think that a psychedelic experience can impart some "Truth" with a capital T that they would otherwise be hopelessly blind to. The reality, though, is that this is all just an experience invented by your brain that can in no way be used as evidence for how the world really is.
To his credit, though, he does largely invalidate most of my complaints via his advice to have many gurus. Since you find him here disagreeing with several people that would be fantastic gurus (in the way he's using the word) it is nearly grounds for dismissing his reasoning immediately just using his own advice.
I don't mean to nit-pick...it's all too easy to find faults in things like this and fail to point out the good. Too often people will point out possible flaws in someone's work and pat themselves on the back for being a good skeptic - so I will say this is definitely a better primer than most on the topic. It just also illustrates the importance of being careful not to be too self-congratulatory that you're such a good skeptic that you begin to blind yourself to your biases and use your new powers of rationality to make yourself dumber by rationalizing instead of looking for what's true.
If you liked this guy's primer on rationality, I'd highly recommend "Rationality: from AI to Zombies" by Eliezer Yudkowsky. It's an extremely long read, but I found it to be absolutely fantastic as it delves deep not only into the pitfalls of normal human reasoning but also into the pitfalls of the aspiring rationalist.
