What do we know? What can we know? Can we even know? These are interesting, and curious questions that human beings have asked themselves for millennia. Unsurprisingly, these are questions that are notoriously difficult to answer. As such, there are people who have proffered some rather peculiar, and, in some cases, downright ludicrous philosophies. French philosopher Rene Descartes tried starting from something we can be absolutely sure of, namely, our own existence, which led to the famous phrase: "I think, therefore I am." Descartes considered the possibility that the real world did not exist and that he was being deceived by a malicious demon. However, he concluded that even if such an outlandish proposition were true, he would still exist. Because if he did not exist, what would the demon be manipulating? What would exist to do the doubting? Contemporary philosopher and theologian Williams Lane Craig offers a humorous anecdote about a bleary eyed student asking his professor whether or not he existed. The professor casually replies, "who wants to know?" The denial of one's own existence is surely absurd, because it simply is not possible to doubt one's own existence.
We can likewise be certain that logical truths entail. For instance, consider the law of non-contradiction, the law of identity, and law of the excluded middle. These state respectively: that contradictory statements cannot both be true simultaneously, an object is the same as itself, and, for any proposition, it can only be true or false. If the statement "I am holding an apple" is true, then it is impossible that the statement "I am not holding an apple is true." There is no possible state of affairs where both statements can be true at the same time. This points us to the law of the excluded middle, either I am holding an apple, or I am not holding an apple. Someone could counter that there is a third alternative, such as I am holding an orange. Yet my holding something that is not an apple does nothing to falsify the statement: "I am not holding an apple." Even if I were holding an object that was not an apple, it would still be true that I were not holding an apple... as I would not be holding an apple!
These are evidently true statements that it simply is not possible to deny, yet there are actually people today who deny them. It is even possible to find scientists who make outlandish statements contradicting these very laws. This only serves to highlight the important of philosophical training, and is also a sad reminder that thinking rationally is something that is still largely neglected. Most of the people nowadays who declare the laws of logic to be false are adherents of a philosophy known colloquially as 'scientism,' which is simply a hangover of verificationism (a defunct philosophy the died off around the 1940s.) These are people who believe that the only way to know something is to verify it scientifically. However, this position suffers from the easy and obvious contradiction, if the statement "something must be proven scientifically for it to be true" is true, then it would have to be scientifically verifiable. Thus, an advocate of scientism must be able to scientifically verify the statement: "something must be proven scientifically for it to be true," which is quite obviously impossible.
When we think of other things we can know, we can know with some degree of certainty that there are minds other than our own. If I am the only person that exists, and other people are just figments of my imagination, then why am I the only person exists? I have only existed for a finite amount of time, and am myself a finite being. I am also a contingent being, and so, as such, there must be at least one thing other than myself. Namely, a necessary being. This was Descartes' rebuttal to the notion that the external world was illusory, the ontological argument. There must exist a necessary being, and since neither Descartes, nor any one of us, are a necessary being, we can be confident that is at least one being that exists apart from ourselves. Whether you call this being 'God' or not matters little, what matters is that there simply IS a being that exists necessarily. The other details can be worked out separately.
We have thus far established that at least ourselves and one other being exists, and that the laws of logic obtain. What other things can we know? The belief that we exist, and that the laws of logic obtain are what philosophers call properly basic beliefs. These are beliefs that we just form intuitively, without inferring them from other beliefs. Whereas, the belief that at least one being other than ourselves exists IS an inferred belief. What other beliefs can we be justified in believing in a properly basic fashion. Perhaps the most obvious one after the examples already given is the reality of temporal becoming. This is the belief that the passage of time is real, and that things really do begin to exist, and cease to exist. This can be contrasted with the belief that everything exists tenselessly, and that the passage of time is an illusion. The latter is obviously incoherent as that, in order for their to be an illusion of temporal becoming, there needs to be temporal becoming.
We can also be sure of the inability of something being able to come into being from non-being, uncaused in any way. It is a properly basic, and intuitively obvious fact that, from nothing, nothing comes. Some might say that it is impossible for nothing, the total and complete absence of being is impossible, yet this reinforces the point that there must exist at least one necessary being. Such, a necessary being, however, must be eternal, yet if time is real then we run into the problem of the impossibility of a beginningless series of events. This has prompted some philosophers to say that God is timeless, which is a perfectly plausible alternative to a God that begins to exist (an obviously incoherent notion.) However, this too has its problems. If God is timeless, how did other things come into being? Given that God is the only being from which more being can arise (being arising from non-being being an incoherent notion), from whence did other beings come? There is a solution to this dilemma, and that is the fact that God was originally timeless, but came into time simultaneously along with the creation of the universe.
Remember that it is only a beginningless series of events that is problematic. A series that begins, but never ends, is perfectly coherent. Some might posit, however, an alternative to God, such as a multiverse, or by positing that the universe is all that exists. The problem with this is that, given that the necessary cause of the universe must have been timeless causally prior to the creation of the universe (and, thus, space and time.) If the necessary cause of existence is non-personal, such as a multiverse, then the universe would have to be co-eternal along with the non-personal cause. Whereas, if the necessary cause is personal, it is freely able to enter into time. Given that there is considerable evidence that the universe began to exist, even if there is a multiverse, it cannot be the necessary cause of everything else in existence, purely for these reasons alone.
What else can we reasonable know or be relatively sure, or certain of? Obviously, there are many arguments for the existence of God apart from the ones I have already mentioned, which establish further properties that the necessary cause of the rest of existence must possess. The purpose of this blog, however, is not to argue in favour of any specific deity, but simply draw attention to the fact that it is an undeniable fact that there is a necessary cause of everything apart from it. People have certainly denied this reality, and the blatantly obvious facts used to support this conclusion, even self-existence, the reality of time, and the validity of logical inference. Yet, these people are clearly and obviously recognised as being irrational, and perhaps even wilfully deluded. For the denial of any one of these truths is absurd, and requires one to believe things worse than magic, such things being able to appear uncaused from non-being, and things that are blatantly contradictory. I do not expect to change anybody's minds, however, but that people would simply make up their own minds, even if they would rather remain intoxicated in their myths.