There are no rules in typography.

This is the hardest fact for people to grapple with when they try to familiarize themselves with the rules, because there aren’t any. We have principles, best practices, and methods that work most of the time, but nothing that works all of the time. We can do our best to ensure that something is durable: good-sized type for reading, plenty of whitespace, pleasing typefaces, and visual appeal, but we can’t account for all environments and devices, which are often in flux.

Learning typography is about figuring out what choices work best for each situation.

Jason Santa Maria.