If there’s one thing we can know for sure, it’s that we cannot know for sure. No matter what belief system or piece of information is in question, in order to think rationally about it we must start with an assumption. We assume that our perception of reality is generally true and we’re not just brains floating around in a big jar and hallucinating everything.
It’s a reasonable assumption; truth matters to us only as it pertains to what we experience. If it were true that everything we experience is imaginary, then absolute truth would be irrelevant in our current lives. What we are concerned with is the truth that affects us…the truth of the world we experience.
Everything you ever know must be filtered through your perception, which is limited and flawed. We tend to ignore this, and work within a “probably not true” to “probably true” scale, and then act like the things on the ends of that scale are absolutes. But in order to know something with 100% certainty, you would need to also know that every possible alternate explanation is definitely false. In order to know that, you would have to know everything about anything related to those scenarios. It snowballs until you realize that in order to know something with absolute certainty, you would need to know everything.
Christians sometimes argue that God knows everything, so if we believe what he tells us, we can know it’s true with absolute certainty. But this is assuming that their God is real, which means they would need to know for sure that every alternative is definitely wrong, which means they would need to know everything in order to know that their God is real.
So whether you’re Christian or Muslim or deist or atheist, the basis of your reasoning is a subjective assumption that you chose to believe (or simply grew up with). We don’t need to worry about that, though. If the most basic assumption of reality is true, how should we go about finding the truth of any other issue? What methods of reasoning would be most likely to arrive at truth?
When you become rigid and stop actively seeking truth, you want what you already believe to be the whole truth. It’s easier that way, because you can just give in to your impulse to cling to what you already think is right, and excuse yourself from any further effort. So having an open mind and the willingness to discard wrong ideas and keep searching is critical.
What does the search look like? You must start with a foundation for your reasoning. Religious people often use their scriptures as a foundation for reasoning; if data contradicts the scripture, then the data is wrong. But I would propose that logic itself is the most solid foundation upon which to base your ideas. Logic is a fundamental trait of our universe, and it is what makes truth of any sort possible. In order for 2 + 2 to equal 4, logic must exist. In order for thoughts to happen, logic must exist. In order for anything in the entire universe to be real, logic must exist.
Perhaps you could say that logic is the substance from which truth is formed. It isn’t so much a thing that exists, as it is an inherent trait of everything that exists, including any possible god or gods. If a sentient god has existed forever, then logic has existed forever, because without it there can be no thought, no reasoning.
However, logic itself does not equal truth. A statement can be logically valid even if the conclusion it reaches is false. Every aspect of an argument must be verified before the logic of it can lead to a true conclusion, which requires making other arguments based on other truths that come from other arguments…
There’s the snowball again. How in the world can we get anywhere?
Suppose I have a pattern of numbers in mind, and I tell you that the number series “4, 8, 16” follows the pattern. If I ask you to give me other sets of three numbers and try to guess what my pattern is, you would likely propose sets like “5, 10, 20” and “2, 4, 8”. And I would tell you that they also follow the pattern. This is called confirmation bias.
At this point you might think, “Well this is easy. It’s just doubling each number to get the next one.” If you keep giving sets of numbers that follow the doubling pattern, you’ll keep getting an affirmative answer that they all follow the pattern.
Even though you would be wrong.
See, if you proposed a series of numbers that does not follow the pattern you already see, such as “2, 17, 63”, I would tell you that it also follows my pattern, and you’ve proven your previous assumption wrong.
If you kept going, and proposed enough varying sets of numbers to rule out possible answers, your pool of “possible truth” becomes smaller and smaller. Thus, no matter which thing in that dwindling pool you end up believing, you are more likely to be believing the truth than you would be if you hadn’t used logic to narrow down the possibilities.
This is what’s so powerful about logic and the scientific method of reasoning. You get closer to the truth simply by looking for evidence that would prove your current beliefs to be wrong. In the real world you don’t have someone like me to tell you what the pattern is. If the only way to know for sure is to rule out every single alternate possibility, then the only way to get closer to knowing for sure is to start ruling them out.
If it turns out that your belief is one of those wrong ideas, discard it and move on. Clinging to falsehood only damages your ability to reason objectively.