noun, verbal noun
You acquire theory after theory. In doing this, you have a lot of theories in your head. You use all these theories as tools for persuasion. These theories will allow you to convince anyone of anything.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. The 説 gets shortened to せっ.
There is no room for persuasion anymore.
They say it would be harder to persuade Koichi of something than it would be to break a rock with your hand.
In order to live in Japan, the first thing I have to do is convince my parents to let me do it.