Be Frightened To Do vs. Frightened Of Something distinguishes two directly documented complement patterns for the adjective “frightened.” Use frightened + to-infinitive for the directly documented infinitival construction; use frightened 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.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use frightened + to-infinitive when the adjective takes its documented infinitive complement; use frightened of + noun phrase when the complement is introduced by the documented preposition.
Key details
Confusion Familyadjective-complement
Rule Familyadjective complementation
Termsfrightened + to-infinitive, frightened of + noun phrase
Choose the right form
Decision table for Be Frightened To Do vs. Frightened Of Something
Meaning / situation
Construction
Decision
fear attached to taking or encountering an action/event
frightened + to-infinitive
use the infinitive construction
fear directed toward an object, situation, or prospect
frightened of + noun phrase
name the object or source of fear
Quick tests
Action-or-object test
Is the fear attached to doing/encountering an action, or to a named object or situation?
If yes: Use “frightened to + verb” for the action/event construction.
If no: Use “frightened of + noun phrase” for the object or situation.
Caveat: This comparison stays within the directly reviewed complement patterns.
Examples
Example
He was frightened to open the door.
The infinitive presents the feared action.
Example
She is frightened of thunderstorms.
“Of” introduces the object of fear.
Example
They were frightened to look over the edge.
The infinitive attaches the fear to the action of looking.
Further guidance
Core difference
Use frightened + to-infinitive for the directly documented infinitival construction; use frightened of + 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.
