>---------------------- Information from the mail header
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>Sender:       Assembly for the Teaching of English Grammar
>              <[log in to unmask]>
>Poster:       ju tianyi <[log in to unmask]>
>Subject:      two questions
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>
>Dear Friends:
>Can any one of you have time to explain the tense in the following sentence:
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>A beam of coherent light one-half inch wide will be three inches wide after
>it has travelled one mile.
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>In the adverbial clause, present perfect tense is used. But, this kind of
>tense is generally used for an action which has finished so far. I think we
>should use future perfect tense because it will be finished after it travels
>one mile. Am I right?
>
>Secondly, In English, all the words have one or more attribution. For
>example, the word "mail" can be a noun, an transitive verb. Then, what about
>"to" when it is used as an indicator of infinitive or infinitive phrases?
>What does it belong to ?
>
>TIA
>
>Tianyi

Tianya, I think your sentence sounds fine with the present perfect.  I
wouldn't want to say "will have travelled . . . . "  Perfect aspect does
often mean completed action.  But it can mean other things as well.  Quirk,
Greenbaum, Svartvik, and Leech wax eloquent (and long) on the various
meanings of tense, aspect, and modality.

As for the "to" with an infinitive, I'd call it a subordinator (like the
"that" which introduces a noun clause}.  But you could probably classify it
simply as the marker of the infinitive.   In that sense, it marks the
infinitive like "be" marks progressive aspect or "have" marks perfect
aspect.

Max Morenberg
Miami University