Observe can take object + bare infinitive or object + -ing in perception/reporting contexts. The contrast commonly tracks whole-event versus ongoing-event perspective, while passive syntax can introduce a to-infinitive.
ReviewedEvidence1 sourceSectionEnglish Usage
Quick answer
Both “observe someone do” and “observe someone doing” are standard: the bare infinitive can present the event as a whole, while -ing presents an action in progress.
Key details
Confusion Familygrammar-and-usage distinction
Rule Familyverb-complement and object pattern
TermsObserve Someone Do, Observe Someone Doing
Further guidance
Boundary
In passive constructions, forms such as “was observed to do” are possible; that is a separate passive pattern from the active object + bare-infinitive contrast.
Construction
Oxford documents observe + object + bare infinitive and observe + object + -ing.
Decision
Use do when you are presenting the observed event as a whole; use doing when you foreground the person in the middle of the activity.
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.
Oxford directly documents “argue somebody into doing something” for persuading somebody by giving reasons. The cited construction evidence directly supports into + -ing; it does not license “argue someone to do” as an equivalent complement pattern.
When ask means request an action from a person, Cambridge documents ask + person + to-infinitive. Bare “ask doing” is not the ordinary request complement for that meaning.
Cambridge directly documents both badger + object + into + -ing and badger + object + to-infinitive for repeated pressure or requests that push someone toward an action. The verb also covers repeated questioning, so context must show whether the sentence is about persistent persuasion or interrogation rather than assuming every use names a requested action.
Cambridge directly illustrates bamboozle + object + into + -ing for deceiving someone so that the person takes an action. The cited entry does not establish bamboozle + object + to-infinitive as an equally documented alternative, so this guide does not manufacture a two-way rule.
Cambridge explicitly documents beg + object + to-infinitive for an urgent request and also records beg for + noun and other request patterns. A following -ing form may appear elsewhere in a sentence, but it is not the ordinary replacement for the documented object + to-infinitive request construction.
Cambridge gives direct evidence for beguile someone into doing something in the literary persuade/attract/deceive sense. The cited entry supports the into + -ing construction; it does not establish beguile + object + to-infinitive as an equivalent pattern for this meaning.
