If you use a pot that’s not large enough, the water temperature will begin to drop. This will result in clumpy, mushy pasta. Additionally, this will create a higher starch-to-water ratio, which causes the pasta to stick together.
In conclusion: Avoid clumpy, mushy, and sticky pasta by using the right pot! Stick to a pot size between 6 and 8 quarts, and fill it up about ¾ of the way for 1 pound of pasta.