A prepositional phrase is a modifier, so it hangs under the word it modifies (Diagrams: Adjectives and Adverbs). It gets two lines: the preposition on a slanted line, and its object on a flat line at the bottom of the slant. The object’s own modifiers hang under it.
Key idea
Hang each phrase under the word it tells about. That is not always the nearest word.
Why it works
The diagram forces the question every reader asks silently: what does this phrase go with? Answering it is how you spot and fix unclear sentences.
Worked example: Not the nearest word
Diagram “Leo kicked the ball over the fence.”
- Baseline: Leo | kicked | ball.
- over the fence tells where he kicked, so it hangs under kicked, not under ball.
- over on the slant, fence on the flat line, the under fence.
Answer: the phrase hangs from kicked
Common mistake
Hanging the phrase under the nearest word instead of the word it modifies. Ask: does it tell which one (hang it from the noun) or where, when, how (hang it from the verb)?