When people say “It’s impossible to know with 100% certainty that there is or isn’t a god.”, I respond that it’s impossible to know with 100% certainty ANYTHING. If “100% certainty” is your benchmark, then nobody knows anything about anything and we can all just give up on ever trying to find any knowledge at all. Obviously, in the real world, we have to make a judgment call and say “In this situation, 99% certainty is good enough for me to make a decision.” or maybe it’s 95%, or 99.999%, depending on the situation. It seems to me an awful lot of time gets wasted quibbling over whether someone who is 99.7% sure the aren’t any gods should be called an atheist or an agnostic.
Even scientific facts (like “water freezes at 32 degrees Fahrenheit”) are subject to change when more evidence comes in. For example, as recent as 20 years ago, it was considered a “fact” that male pattern baldness was caused by a sex-linked gene on the X chromosome. Now we know that the original study which made that determination was faulty. The “fact” that you inherit baldness exclusively from your mother’s side of the family turns out to be simply not true.
Even the example of water freezing at 32 degrees F isn’t 100% true. The truth is more complicated than that, depending not just on temperature but also pressure. The so-called triple point of water happens at .01 degrees C and 611.73 Pa (roughly .006 atmospheres). Around 2,000 atmospheres, water can remain liquid all the way down to zero Fahrenheit. Read the wikipedia article about “ice”.
Heck, even in an ordinary real-life setting, if you put a bowl of water outside and the meteorologist on the radio tells you that it’s 31 degrees outside, can you be 100% sure that the water will freeze? Of course not. The weather report could be mistaken. The water could have trace amounts of salt in it, which changes the freezing point. The bowl might be in direct sunlight, preventing it from freezing.
And in the bigger picture, the only reason that you think you know that water freezes at 32 degrees F is that you remember having been told this fact by other people. But you can’t be 100% certain that your memory is accurate. People forget things all the time and make mistakes. Maybe the correct number is 23 and not 32 but you have some combination of Alzheimer’s disease and Dyslexia. Sure, the chances of that being true are very very slim but it’s not zero.
Beyond faulty memory, there’s also the possibility that you are not who you think you are at all and everything you think you remember about your past is actually an elaborate hallucination. You could be lying in a hospital bed, in a coma, on some distant planet, dreaming that you’re an Earthling, and all the so-called facts you think you learned on Earth are just figments of your imagination. Sure this idea seems far-fetched, but you can never be 100% certain that it isn’t true.
I’m not saying that facts don’t exist, or that nothing is true. I’m just saying that, as a human being, our knowledge of the facts is never 100% certain.
The only fact I can think of that might come close to being 100% certain is Rene DesCarte’s Cogito Ergo Sum, “I think therefore I am”. But even that statement is very limited. It only applies to the person who is doing the thinking. And it doesn’t really explain what it means to exist. If I’m part of a simulation, living inside a computer, is it fair to say that I “am”? Cogito Ergo Sum doesn’t even prove that your brain has any physical substance, let alone the body which you believe contains your brain. It also doesn’t explain what I am. It just says that I am. And I’m still not entirely convinced that it’s 100% certain. Maybe there’s a flaw in the logic that we haven’t discovered yet.
But most of the time, in day-to-day life, it’s pointless to worry about this stuff. All you need is to be convinced that it’s probably okay and the risks are small. Could a speeding car kill you? That’s a sizable risk, so it’s prudent to take precautions like staying on the sidewalk and waiting for the signal at the crosswalk and looking both ways before crossing the street. But it would be overreacting to never leave your house just because you can’t be 100% sure that a car won’t drive up onto the sidewalk and kill you. There are no guarantees in life. Just accept the fact that, sooner or later, everybody dies, and make the best judgment calls you can in each situation. If you spend your life terrified of death, you miss your chance to enjoy the life you have.