We have no choice but to go on with our lives in the present, pushing into that tiny little bit of the future that our “now” slides into, without thinking about any of the things you’re saying—not because they aren’t worth thinking about (it would be wonderful if we could) but because we have no way of thinking about them, nothing to think about them with.”
Ultimate questions, Bryan Magee
Why were the word "with" placed in the end of the sentence. What is the role of it?
You have a relative clause that could be written thus:
we have . . . nothing with which to think about them
In a clause like this one, it is perfectly normal to postpone the preposition ("with") and delete the relative pronoun ("which"):
we have . . . nothing to think about them with
You may be interested in the following:
https://en.wikipedia.org/wiki/Preposition_stranding (see the example sentence "this is the book I told you about")
A question on relative clause (see example sentence #2)
Who / whom : The guests whom we were talking about have come are my brothers-in-law (Gary Botnovcan's answer)
The word "with" is a preposition. It has many uses. See Cambridge on "with"
One meaning is "using".
We use with to refer to what we use to do something:
- They opened the package with a knife.
- I’ll tie it with some tape to keep it closed.
- He cleaned the table with a cloth he found in the kitchen
From this meaning one might formulate the phrase:
... we have nothing with which to think about.
This includes a relative clause, headed by "which:. That clause can be reduced and inverted, resulting in:
... we have nothing to think about them with.
Thus "with" in this usage is a preposition indicating a thing to be used for a purpose. In this case, the unspecified thing (that the author says we do not have) to be used to "think about them".
