The final three politeness levels we've yet to talk about are 하소서체, 하오체, and 하게체. These forms are still commonly found, but not in modern-day speech. Instead, you can find them in older materials, as well as Korean historical dramas. So they're really useful to know, but are also large topics on their own so we only have time to briefly introduce them. Be aware of them, but knowing how to create grammar for them is less important (unless you're trying to write a historical drama).