I’ve just started learning logic, and I understand that valid inferences come from rules of inference, one of them being modus ponens. But what I don’t understand is why we accept these rules as valid in the first place (the same question applies to the others). I know it would be circular or pointless to try to prove them using logic itself, I started this 1 week ago, so experts of Reddit, bear with me.
People are constantly seeing things in the world every day. They see an apple, a tree, a star, or a bacterium. They hear a strong sound, or maybe a thought pops up in their minds, and they start noticing that all these things have something in common.
If I show you a cow, a person, or a planet, your mind already knows what they are. You probably know what these things have in common. It is in your mind: a categorization or a pattern that your mind already uses for surviving and recognizing things across the universe.
You can use any tool you have—a pencil or a reed—and assign a symbol to this. It could be a simple line, a dot, or maybe the symbol “1” to represent this idea on paper or clay (like our ancestors did), and voilà—you have the number 1.