Thankfully, mathematicians didn’t have to categorize every single possible knot you can tie in a piece of string: they already knew that there are prime knots. The area of maths dedicated to investigating knots is known as knot theory (with the mathematicians involved called knot theorists) and, much as the area of number theory uses prime numbers to learn about all the other numbers, knot theory is only really worried about prime knots, because, if we understand them, we are within reach of understanding all knots.
