Difference between "less" and "lesser"? [closed]

Less refers to quantity, lesser refers to quality.

Your sentence could be rephrased as "substitute less punishment for more punishment." Here we are saying that the amount of punishment is smaller. But if you say "substitute the lesser punishment" you are saying the type of punishment is not as severe.

• Forty lashes is less punishment than 100 lashes.
• Being pelted with rotten tomatoes is a lesser punishment than being pelted with rocks.

Consider:

• less of the two - a smaller amount of both things under consideration: "I would prefer to see less of the two in the future."
• lesser of the two - the thing that is smaller in quantity, amount, stature, etc. than the other: "I'll take the lesser of the two and you can have the other one."

One way to look at it, then, is that less refers to an amount of something that need not be compared to anything else, whereas lesser refers to the thing itself in comparison to something else (which need not be explicitly named).