Dear Joan Skliar:

You wrote:

>>Why do we change “too” to “so” when using “should have”?
>>Ex: He bought too much popcorn at the movie. He shouldn’t have bought so much popcorn at the movie.
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They mean two different things. You could certainly say “He shouldn’t have bought too much popcorn,” but it means something else. Ditto with “He bought so much popcorn.”

Too means “excessively.”

So in this sense means something akin to “thus,” “such,” or “in this or that way.” In other words, saying “so much” you are indicating either that the listener is aware of how much popcorn he bought, or you are going to tell him. For example, “He bought so much popcorn that he had to throw half of it away.”

Do you recall the scene in the film Casablanca with the two Dutch refugees who are fleeing to America and trying to teach one another English? When told that it is ten o’clock (or “ten watch”), one of them says “Such much?” She should have said “So much?” or “So late?” but the reply does illustrate what “so” means in this sense.

Either sentence works fine with either word, but they have two different meanings.