Argumentum a fortiori

Argumentum a fortiori is a big phrase that means if something is true in a certain situation, then it must be even more true in a different situation. Let's say you're trying to convince your friend to take a bath. You might say, "If you get dirty playing outside for just an hour, imagine how dirty you'll get if you play outside all day!" That's an argumentum a fortiori because you're using something that's true (getting dirty after an hour of playing) to convince your friend that something else is even more true (getting even dirtier after playing all day). It's like saying, "If we know a flower needs sunlight to grow, then a giant tree must need even more sunlight to grow."