Dictionaries attempt to explain a difference, but common language seems to prefer the single word, unless interrupted by something like “single” or in the phrase “each and every thing.”
As two words, “every thing” counts each one individually.
As one word, it refers to the entire collection in its wholeness. It refers to all of the things in that one word.
In choosing one or the other, the writer should consider the message to be conveyed, the difference being if the individuals matter.
- As I looked around my teenager’s room, every thing she owned was put in its proper place or was buried in a drawer where I could not see it. I even looked under her bed.
- (Two words = each individual item)
- I couldn’t believe it. Everything I had taught her had now been absorbed.
- (One word = the totality of what I had taught her)
- Do you remember every thing your mother said? I don’t.
- (Two words= each individual teaching)
- But sooner or later, everything clicked into place.
- (One word = the totality, it all clicked)