Be Fascinated To Do vs. Fascinated By Something distinguishes two directly documented complement patterns for the adjective “fascinated.” Use fascinated + to-infinitive for the directly documented infinitival construction; use fascinated 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.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use fascinated + to-infinitive for the directly documented infinitival construction; use fascinated by + noun phrase for the separately documented prepositional construction.
Key details
Confusion Familyadjective-complement
Rule Familyadjective complementation
Termsfascinated + to-infinitive, fascinated by + noun phrase
Choose the right form
Decision table for Be Fascinated To Do vs. Fascinated By Something
Meaning / situation
Construction
Decision
interest/surprise presented through an infinitive event
fascinated + to-infinitive
use the documented infinitive construction
object or cause of fascination
fascinated by + noun phrase
name what holds the interest
Quick tests
Event-or-object test
Are you presenting what someone is fascinated to learn/see, or naming the object/cause of fascination?
If yes: Use “fascinated to + verb” for the infinitive event.
If no: Use “fascinated by + noun phrase” for the object/cause.
Caveat: Keep the comparison to the attested patterns; closely related adjectives may behave differently.
Examples
Example
I was fascinated to learn how the mechanism worked.
The infinitive presents the event of learning.
Example
The students were fascinated by the demonstration.
“By” names the object/cause of fascination.
Example
She was fascinated to discover the hidden compartment.
The infinitive introduces a discovered fact or event.
Further guidance
Core difference
Use fascinated + to-infinitive for the directly documented infinitival construction; use fascinated 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.
