you scratch my back and I'll scratch yours
see scratch one's back.
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Itch vs. Scratch: What’s The Difference?Okay, this one might make you feel a little itchy. An itch is a skin irritation that causes the desire to scratch. Scratch describes the action used to relieve an itch. The grammatically correct construction is “to scratch an itch.” People often use itch and scratch in place of each other in everyday speech. For example, you may hear people saying they need to “itch …
Should You Say “Between You And I” Or “Between You And Me”?Why are there different ways of saying the same thing? Grammar is a combination of rules and conventions. What’s the difference? Well, the rules are things like a verb must agree with its subject. By that rule, “he say” is incorrect. Then there are conventions, which are uses of language that are common enough that even though they break the “rules” they become “correct” simply …
The American Heritage® Idioms Dictionary
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