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Hi! Sentence 1 means an action in the past. Sentence 2 means an action in the recent past at an indefinite time and the action is completed or close to completion. Are my interpretations correct? Thanks, Fulvio

1. I enjoyed reading this book.

2. I have enjoyed reading this book.

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Yes, that's the broad idea.

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yellowstarstruckand the action is completed or close to completion.

In your examples the action in sentence 1 is no less complete than the action in sentence 2. Completion (or not) is not always a good way to differentiate between those tenses. In fact, I'd guess that on average the simple past expresses a completed action more often than the present perfect.

CJ