Putting on them

There is a funny syntactic quirk of English: you have to be a full noun phrase (i.e. not a pronoun) to follow certain particles. So:

You put on the shoes.
* You put on them. ("*" = "not grammatical" in standard English.)
You put them on.

You picked up the book.
*You picked up it.
You picked it up.

Carter hasn't gotten this one down yet; he says things like "You put on them" all the time. (Only, he means "I [Carter] put them on", technically, because he still has "I" and "you" switched too...) I can almost see those gears churning in his active little head; many linguistic puzzles still to solve. In the meantime, a conversation about who is going to put on the shoes gets confusing fast!