Two different answers for a question say that 'd in "How'd you know?" is a contraction of did.
Can I always use 'd as contraction of did, or should I use it only when 'd follows a word that is part of a set of words?
For example, could I write "I'd know it." or should I write only why'd, who'd, where'd, when'd, and how'd?
I checked the NOAD, but it says that 'd is a contraction for had and would; the same is said from the OALD, which says that he'd is a short form for he had or he would. Both the dictionaries didn't help to understand when I could use 'd instead of did.