"Run by this" sounds like a reasonable shortcut, which is exactly why it's a common mistake. It's wrong: the object of this idiom has to sit between "run" and "by" or "past," never after the preposition.
The error
Learners who know "run this by you" sometimes drop the object and move it after the preposition instead, producing "run by this" or "run past this" when they mean "check this with someone."
Wrong: "I'll run by this before sending it." Right: "I'll run this by you before sending it."
Wrong: "Can you run past this with the team?" Right: "Can you run this past the team?"
Why the object placement matters here
Without the object correctly placed, "run by" collapses into a completely different, unrelated meaning: stopping by a place briefly ("I'll run by the office"). "I'll run by this" doesn't read as "I'll check this with someone" -- it reads as a plan to physically stop by something called "this," which rarely makes sense and forces the listener to guess what you meant.
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Start learning for free →The idiom's whole grammatical signature depends on the object sitting in that middle slot: run [object] by/past [someone]. Omitting it, or moving it to the wrong side of the preposition, breaks the sentence rather than just sounding slightly off.
A simple test to check your own sentence
Before sending a message, check that there's a named thing -- an idea, the draft, the numbers, "this," "it" -- sitting immediately after "run" and immediately before "by" or "past." If that slot is empty, or if you find yourself writing "run by/past" followed straight by a noun with no object in between, you've dropped into the wrong construction.
The rule
The object is never optional in this idiom, and it never moves to the far side of the preposition. Say what's being checked right after "run," then name who you're checking it with after "by" or "past."
Practice scenarios
Practice this pattern in situations like:
- rewriting "run by this" as "run this by you"
- catching a dropped object before sending a message
- distinguishing this idiom's "run by" from the unrelated "stop by" meaning
Useful practice phrases:
- "Let me run this by you before I send it."
- "Can you run the numbers past finance?"
- "I ran it by legal yesterday."
The object always goes in the middle -- never at the end, never missing.
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