"Anything" and "any thing"

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What is the difference between "anything" and "any thing"?

The short answer is that it is nearly always better to use anything.

Anything, which means “a thing of any kind,” can be used in many more contexts than any thing, which is rarely used at all. Below are some examples of the ways that anything is used. 

• We were allowed to do anything we wanted to. 
• If you're not sure what to say, just say anything that comes to mind. 
• She didn't say anything at all. [=she said nothing at all] 
• That dog will eat almost anything. 
• I'll do anything I can to help. 

The only possible contexts in which you might want to use the two-word version, any thing, would be:

1) when you want to emphasize that you are referring to an object, as opposed to a person, animal, or idea

2) when things is plural

3) when you want to insert an adjective before thing

Below are some sentences in which any thing would be appropriate. 

• You are not allowed to take pictures of people, but you can take a picture of any thing (or things) that you see. 
• Any things left on the floor will be put in the garbage. ("Anything left on the floor will be put in the garbage" is also correct.) 
• She criticizes me for any little thing that I forget to do. 

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