Quote:
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Although "yesterday" and "before" both are adverbs of Time modifying "have seen", the meanings are very different.
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On the contrary,
'before' is not an adverb of Tense. :D That's why it's compatible with the Present Perfect.
"I have seen Simon before/previously" (OK)
'yesterday' is an adverb of Tense, and the reason why it's not compatible with the Present Perfect.
"I saw Simon before." (not OK)
Adverbs denoting time are divided into two groups:
1) adverbs denoting specific time, called Tense/Time (i.e. yesterday)
2) adverbs denoting non-specific time, called aspectual (i.e. before)
Adverbs belonging to group 2) are compatible with the Present Perfect
Aspect.
In general,
Tense modifies Tense (Simple Past)
Aspect modifies Aspect (Present Perfect)
:D :D :D