That’s the remedial stuff. Here’s an advanced course in confusing word pairs.
1. Everyday/every day
Contrary to what you see practically every day, these are two different concepts. Everyday is an adjective that means ordinary or commonly occurring, while every day means each and every single day.
Sly and the Family Stone assure us that in spite of the band’s fame and lifestyle, the members remain “everyday people.” Elvis Costello, unfortunately, gets it wrong when he sings, “Everyday I write the book.” Clearly he means every day. Who knows how many record sales this cost him?
[For more on everyday vs. every day, read: “Simple tricks for avoiding a common language error“]