Q: What is the difference between “each” and “every,” as in “Each time I visit my mother, I get a headache,” or “Every time I visit my mother, I get a headache”?
A: “Each” means one of two or more people (or things), considered individually. “Every” means all the members of a group, without exception. The words may seem to mean the same thing in a larger sense, but there are nuances of difference. “Each member of the choir” is considering all of them one by one; “every member of the choir” is considering them as a collection, one from which no member is excluded.
When you say, “Each time I visit my mother, I get a headache,” you’re thinking of headache after headache after headache, with each individual visit. When you say, “Every time I visit my mother, I get a headache,” you’re stating a rule—something that happens without exception.
Again, the difference is very small but worth preserving, I think. And by the way, the expression “each and every time,” which some usage experts consider a misuse (or a redundancy at best), is pretty common these days and of course combines both meanings.