Cambridge directly documents busy + -ing for being occupied with an activity, and separately documents too busy to do something. Busy doing and too busy to do are different constructions with different meanings. Do not treat bare busy to do as a direct alternative to busy doing.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Use be busy + -ing for the activity occupying someone; use too busy to + infinitive only for the distinct meaning that busyness prevents another action.
Key details
Confusion Familyverb complement choice
Rule Familyverb complement licensing
TermsBe Busy Doing, Busy To Do
Further guidance
Boundary
Busy doing and too busy to do are different constructions with different meanings. Do not treat bare busy to do as a direct alternative to busy doing.
Construction
Cambridge directly documents busy + -ing for being occupied with an activity, and separately documents too busy to do something.
Decision
Use be busy + -ing for the activity occupying someone; use too busy to + infinitive only for the distinct meaning that busyness prevents another action.
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.
busy↗ (opens in a new tab)Cambridge University Press & Assessment · Preferred lexical authority directly documenting busy doing something and the distinct too busy to do something construction.
Cambridge directly gives accustom yourself to followed by an -ing form for becoming familiar with new conditions. The to belongs to the prepositional construction accustom yourself to something; do not infer an equivalent to-infinitive from the surface word to.
Oxford documents apply yourself to (doing) something for working hard and attentively at a task. This apply-yourself construction takes prepositional to; other senses of apply use different complements and should not be merged into this pattern.
Cambridge directly documents capable of something/doing something for having the ability, power, or qualities needed to do something. The documented adjective complement is capable of + noun or -ing form; do not replace the prepositional complement with capable to + infinitive on the basis of meaning alone.
Cambridge directly documents be good at something/doing something for being skilled or successful at an activity. Good to + infinitive can occur in other constructions and meanings, but it is not a substitute for the documented skill construction be good at + -ing.
Oxford directly documents reduce somebody/something to (doing) something, usually in the passive, for being forced into a worse state or action. Here to introduces the resulting state or activity; the authority does not establish an equivalent be reduced to + bare infinitive pattern.
Cambridge directly documents be skilled at/in doing something for having developed ability in an activity. The preferred-source construction uses a preposition before the -ing form; do not infer skilled to + infinitive as a parallel complement solely from the adjective’s meaning.
