An illusion is something different from the truth. But what is the truth? What can we say we know for sure? Descartes, the famous philosopher and mathematician, famously concluded that we couldn't be absolutely sure that even the most obvious mathematical evidences were true, since we could always suppose that some evil genius could be constantly making us see as obvious something that is not true. This radical doubt can be easily be made believable in movies like The Matrix and, to a lesser extent, Total Recall and many others.
A contemporary philosopher, Nick Bostrom, even argues that, given the current patter of technological evolution, it is more likely that we are living inside a simulation, for given the number of intelligent civilizations and their ability and desire to create simulations of the world, there should be many more simulated worlds than "real" ones.
So, what do we know for sure? Well, Descartes concluded that the only thing one could know with absolute certainty was one's own existence. Although what "one" or "I" (or "cogito") means is clearly unclear. Also the notion of "existence" is at most clearly vague. What does it mean "to exist"?
Descartes answered that these were self-evident notions and that attempting to clarify them would be fruitless. To me this seems a way to simply get by without really answering the fundamental questions or even recognizing that there are such questions.
As skeptical philosophy have shown us, there is in fact little we know for sure. Science, by allowing a vision of the world much more vast and complex than ever before, has provided a plausible explanation for that: we are fragile, very limited, biological creatures, that have just discovered, as a species, some rudiments of how the world works. This has given us mobile phones, space telescopes, computers and so on. But just think, in a universe with billions of years, where will scientific progress take us in a mere few million? Certainly the expanded minds and senses of our successors will be able to see much farther, understand much more than we have ever come close to.
To distant future civilizations, just a few million years from now, we must seem like monkeys seem to us. In fact, it seems we have separated from them a few million years ago. So we don't even need the idea of exponential evolution to understand why our current vision of the universe is so limited.
Seeing us just at the beginning of the journey of exploring the universe's laws and circumstances easily explains why we have so many doubts. Although, of course, one of these doubts is if science as a whole, or the universe as a whole, is not some simple gigantic illusion.
It is easy to see then, with all these doubts and uncertainties, why we need belief, faith. Because, if we rejected as a basis for action anything in which there was even the slightest reason for doubt, we would probably have to reject everything. Even the cartesian "I think therefore I am" would be of little significance, for we wouldn't know what "I" and "am" implied to our practical action.
Descartes, for instance, fond out that, although he could not trust even the plainest mathematical evidences, he could believe that he existed and also that Absolute Perfection also existed, because, contrary to every other idea, the idea of Absolute Perfection, when contemplated, implied its own existence. This argument, so strange, can only be accepted on mystical grounds, in my opinion. It's like saying: "I saw God, and now I can no longer doubt that He exists, although everything else I saw might be an illusion."
This is really not an argument, it is simply a statement derived from a personal and unsharable experience. So, whatever one may derive from it it certainly should not have any influence on others (in fact it should be unintelligible for anyone not having had that experience).
But, even having had that experience, one should distinguish the existencial evidence from the logical evidence. I mean, I can see my girlfriend, look her in the eyes and I simply know what she is feeling. But this word "know", is not at all like the word know in "I know that 2+2=4" or "I know that Mars has a red atmosphere". I have no way to prove to myself that I "know" what she feels. In fact, she might be a robot. But, existentially, I know how she feels and that she indeed feels. I cannot prove it though, not even to myself. Logically, it might be an illusion. But, existentially, my will is part of a world much vaster than concepts can grasp, and, in that world, I "see" or "intuit" many things that serve as basis for my actions and that I cannot put into theory.
Of course, it would be easy to say that all those "certainties" or non-conceptual "knowledge" (if that is the right word for that) is just our limbic system playing tricks on us. We feel all those certainties because billions of years of "evolution" have imprinted them in our brain. They are (or at least were) important for our survival and so we feel them as sufficient basis for action. Thus, this God's presence, that might seem so unquestionable, may be nothing but a genetic program running in our brain to keep us going, through the jungles of life, trusting our friends, being ready to kill and die for the group, and so on.
All this just points out, once again, how lost we are in terms of certainties. Is it God or simply a hormone, some cells firing up in the brain? We don't know, either way.
With all this uncertainty we would not able to do anything at all. So how are we able to do anything? Well, I think most of us just accept something as true. It might be a working hypothesis, it might be a pledge, it might be something which we feel it is wrong to doubt. In fact that is what distinguishes the critical from the dogmatic thinker. The first questions every hypothesis, the second avoids every doubt. But none can pass without the assumptions that make life and action possible. The only difference is that one looks at this assumptions like passing landscapes, that can always be revised and updated to better ones, while the other holds on fiercely to the certainties he holds and despair at the prospect of being shown wrong.
Of course, seen in this light, there are both critical and dogmatic thinkers in every area: science, religion, politics, sports, etc. It is not a question of the area in which you are in but whether you accept or not that, in the end, it's all hypothesis, we don't really know anything at all. It is incredibly frequent for instance, to see societies of so-called skeptics that deny without research all findings of "paranormal" or "supernatural" or "spiritual" activity. In this perspective, those that deny without researching are dogmatic, the fact that they do it in the name of skepticism, religion or science is of no difference whatsoever.
But, of course, in general, we tend to be dogmatic thinkers when we can't conceive that reality can be very different things. Conversely, when we start to see all those different perspectives or hypothesis that would explain reality, than our happiness starts coming, more and more, not from a specific vision of reality, but from the mystery and articulation that all these perspectives have. Like a necker cube with more that a thousand faces.
It is easier to be happy as a critical thinker.
So, our job in the next sub-chapters is not so much to unmask perceived truths as illusions (in fact everything we think we know might be an illusion), but to show the role that each theory, or vision of life, has or might have. By doing this theories will work for us, either as passing intruments or simply to give us contemplative pleasure, instead of being the simultaneously help and entrapment they usually become to most of us.