I've recently come across this sentence:
The young Nietzsche will have come across the term Kreuzspinne in his German edition of Emerson's The Conduct of Life.
I'm confused as to why the author used the simple future perfect form "will have come" instead of the future perfect form in the past "would have come", since we're obviously talking about the past.
The future is sometimes used to make predictions, and your sentence is an example of a prediction about the past:
We can use the future perfect tense to make a present prediction about something that we believe has or should have happened in the past. (FreeDict)
The young Nietzsche will have come across must not be regarded as placed in the present or future because of will. It basically means The young Nietzsche probably came across... or The young Nietzsche must have come across...
This other site explains the same:
A common use of will is for making predictions. However, predictions aren't only for the future. With the future perfect, you can predict what happened before now (in the past). For example:
- She's driving a new BMW. That won't have been cheap! = I'm sure that wasn't cheap!
This is the epistemic sense of 'will', not the future. The situation (Nietzsche coming across the term...) clearly took place in the past. The idea is that the writer is making a strong guess about a past situation, and hence has decided to use 'will' instead of 'would'. The meaning is similar to 'must'.
Though this use of 'will' typically implies some chance of future confirmation of the writer's guess, there is here a clear lack of any future interpretation, as it is exceedingly unlikely that any guess about young Nietzsche is confirmed in some future scenario.
5—used to express probability and often equivalent to the simple verb
that will be the babysitter
