How much better would a passphrase be if you swapped the first letters of each word with a shift to the left:
"correct battery horse staple" becomes "borrect hattery sorse ctaple"
This would be simple to remember because you know all the words but how much harder would this be for an attacker?
Further, we could try this with the first and last letters of each word producing:
"torrecb yatterh eorss etaplc"
(This at least reduces the chances that swapping the first letters will still result in normal English words, like 'hattery' in the first example)
How much harder would this make it to crack, is it worth the extra effort to remember?
Do dictionary attacks consider things like this?