The primary difference between placing a Prepositional Phrase (PrepP) under the VP versus under the ADVL node comes down to whether the phrase is a complement (required) or an adjunct (optional).
According to the analysis in The Grammar Book, here is how that distinction works:
When the PrepP is under an ADVL node, it is considered a circumstance adverbial. These are optional pieces of information that provide context like time, place, or reason, but the sentence is grammatically complete without them.
Example from the book: "Jason ate dinner at four o'clock" Chapter 25 - Adverbials.pdf.
Reasoning: Jason can "eat dinner" by itself. The time (at four o'clock) is an extra detail, so it gets its own ADVL branch as a sister to the VP.
When a PrepP is placed directly under the VP node, it is usually because it is required to complete the verb's meaning. In these cases, the verb and the prepositional phrase are semantically "glued" together.
Example from the book: "She put her coat on the chair" Chapter 25 - Adverbials.pdf.
Reasoning: You cannot simply say "She put her coat." The verb "put" requires a location to be complete. Because the PrepP is mandatory, it is analyzed as part of the core VP rather than an external ADVL.
| Feature | PrepP under ADVL | PrepP under VP | | :--- | :--- | :--- | | Category | Adjunct / Circumstance Adverbial | Complement | | Necessity | Optional (extra info) | Required (completes the verb) | | Relationship | Modifies the entire event | Completes the verb phrase | | Visual Scope | Sister to the VP | Inside the VP |