When to use "rather than" versus "instead of"?

Solution 1:

Let's try some minimal pairs:

• I walk rather than run

• I walk instead of running

• I eat apples rather than oranges

• I eat apples instead of oranges

• I walk quickly instead of quietly

• I walk quickly rather than quietly

I don't really think there's much of a difference, except perhaps rather than implies preference whereas instead of implies substitution. But that might be nitpicking. And it doesn't seem to apply when using it to coordinate adverbs (last pair).

Also, there's a slight difference in the verb forms in the first pair, but there's not really a difference in meaning there.

Solution 2:

"Rather than" is coordinating. "Instead of" is subordinating. As the above examples indicate, while the distinction when it's a matter of nouns or adverbs might be moot, the verb forms on either side of "rather than" are the same, while "instead of" takes a participle. Getting them mixed up in formal writing could easily confuse a reader about the nuances of the argument.