Be Startled To Do vs. Startled By Something distinguishes two directly documented complement patterns for the adjective “startled.” Use startled + to-infinitive for the directly documented infinitival construction; use startled by + noun phrase for the separately documented prepositional construction. The page stays within those attested patterns and does not infer a broader rule from synonymy.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use startled + to-infinitive when the adjective takes its documented infinitive complement; use startled by + noun phrase when the complement is introduced by the documented preposition.
Key details
Confusion Familyadjective-complement
Rule Familyadjective complementation
Termsstartled + to-infinitive, startled by + noun phrase
Choose the right form
Decision table for Be Startled To Do vs. Startled By Something
Meaning / situation
Construction
Decision
surprise or alarm linked to an event expressed as an infinitive
startled + to-infinitive
use the reviewed infinitive construction
the person, sound, event, or thing that causes the startle response
startled by + noun phrase
use “by” to name the cause
Quick tests
Event-or-cause test
Are you presenting the startling event through an infinitive or naming the cause directly?
If yes: Use “startled to + verb.”
If no: Use “startled by + noun phrase.”
Caveat: These examples illustrate the reviewed patterns without claiming that they exhaust every construction with “startled.”
Examples
Example
I was startled to find the office empty.
The infinitive presents the event that prompted the reaction.
Example
I was startled by the sudden alarm.
“By” names the cause of the reaction.
Example
She was startled to hear a crash and startled by the silence that followed.
The example separates event from cause.
Further guidance
Core difference
Use startled + to-infinitive for the directly documented infinitival construction; use startled by + noun phrase for the separately documented prepositional construction.
Style Boundary
Treat this as a comparison of directly documented complement patterns, not as a claim that every other complement is impossible. Choose the construction that matches the intended grammatical relationship.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
Be Afraid To Do vs. Afraid Of Something distinguishes two directly documented complement patterns for the adjective “afraid.” Use afraid + to-infinitive for the directly documented infinitival construction; use afraid of + noun phrase for the separately documented prepositional construction. The page stays within those attested patterns and does not infer a broader rule from synonymy.
Be Alarmed To Do vs. Alarmed At Something distinguishes two directly documented complement patterns for the adjective “alarmed.” Use alarmed + to-infinitive for the directly documented infinitival construction; use alarmed at + noun phrase for the separately documented prepositional construction. The page stays within those attested patterns and does not infer a broader rule from synonymy.
Be Amused To Do vs. Amused By Something distinguishes two directly documented complement patterns for the adjective “amused.” Use amused + to-infinitive for the directly documented infinitival construction; use amused by + noun phrase for the separately documented prepositional construction. The guide stays within those attested patterns and does not infer a broader rule from synonymy.
Be Annoyed To Do vs. Annoyed About Something distinguishes two directly documented complement patterns for the adjective “annoyed.” Use annoyed + to-infinitive for the directly documented infinitival construction; use annoyed about + noun phrase for the separately documented prepositional construction. The page stays within those attested patterns and does not infer a broader rule from synonymy.
Be Astonished To Do vs. Astonished At Something distinguishes two directly documented complement patterns for the adjective “astonished.” Use astonished + to-infinitive for the directly documented infinitival construction; use astonished at + noun phrase for the separately documented prepositional construction. The page stays within those attested patterns and does not infer a broader rule from synonymy.
Be Astounded To Do vs. Astounded By Something distinguishes two directly documented complement patterns for the adjective “astounded.” Use astounded + to-infinitive for the directly documented infinitival construction; use astounded at/by + noun phrase for the separately documented prepositional construction. The guide stays within those attested patterns and does not infer a broader rule from synonymy.
