Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

THE PAST PERFECT AND THE PAST SIMPLE 

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Sometimes the past perfect may be necessary to resolve possible

misunderstanding or ambiguity as regards the sequence of events and the

semantic relationship between them:

They all left the room when she 

recited her poem. 

(suggests they all left the moment she started reciting)

They all left the room when she

’d recited her poem. 

(suggests they left after she’d finished reciting)

620 | Past time

Cambridge Grammar of English

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The past simple often suggests a more immediate causal link between two events,

compared with the past perfect:

When he opened his desk, he discovered a dead bird. 

(stresses the immediate result, rather than ‘When he had opened his desk …’)

When he’d opened his third present, he looked at the roller skates and smiled. 

(not such an immediate or direct relationship; the roller skates may not have

been in the third present)