Dave's ESL Cafe's Student Discussion Forums

[puzzle]

Dear teachers,
Can you help me with the following sentence?
The sailors used the sun overhead to navigate by.
What member of sentence is "to navigate by"? Can "by" be omitted?
because we say " We use knife to cut meat", but not " we use knife to cut meat with"?
So can you explain the differences between the two sentences?
Thank you very much!

[Mary W. Ng]

Question:

"The sailors used the sun overhead to navigate by."
What member of sentence is "to navigate by"? Can "by" be omitted?

Answer:

"To navigate by" is an infinitive phrase functioning as an adverbial modifier of purpose; the infinitive phrase modifies the verb "used".
.
"By" is used to show how something is done; "use" means to put something to a particular purpose. You don't need two words to express the same idea; I would say "by" is redundant in the sentence and should be omitted.

"By", however, is needed in the following sentence:
"The sailors navigated by the sun and the stars."

The same reasoning can be applied to the second sentence.

I hope this helps.
_________________
Mary W. Ng
Helping students learn grammar
http:www.aimpublishing.com

[lotus]

It is a dangling preposition. Grammarians shun such use. However, there are times when it is appropriate.

Why was the helmsman staring at the lighthouse?
He actually uses the light from the lighthouse to navigate by.

If you omit the "by", it becomes more of a statement and less of an answer of why and how.

Of course, you can avoid the dangling preposition altogether by saying:
He actually uses the light from the lighthouse for navigation.

In most cases, the dangling preposition is in fact redundant. Your second example is such a case. Putting "with" at the end is not only redundant, it makes the statement sound trite.

We use a knife to cut meat.
We use a knife to cut meat with.

For more information on dangling prepositions, see the links below:

http://grammar.ccc.commnet.edu/GRAMMAR/prepositions.htm#ending
http://everything2.com/title/Dangling+preposition


--lotus
_________________
War does not make one great --Yoda