1. We should arrive before dark.
2. I should have finished the book by Friday.
[In the Oxford dictionary, I saw the two sentences. They mean 'guessing.'
What is the similar expression for #3 in American English? Would you check the following?]
3. I would have finished the book by Friday.
4. I will have finished the book by friday.
1. OK
2. This sentence means "I ought to have finished ... , but I didn't."
3. This sentence is making an excuse to explain why he/she didn't finish the book by Friday.
4. This sentence is stating that he/she will be finished reading the book by Friday.
The similar expression for sentence #3 in American English would be:
3. I would have finished the book by Friday.
American English often uses "would have" to express a guess or speculation about a past event, similar to the use of "should have" in the first two sentences. It indicates a hypothetical situation or an unrealized possibility in the past.
Regarding sentence #4:
4. I will have finished the book by Friday.
This sentence is in plain future tense, expressing a definite statement about completing the book by Friday. It does not imply any guessing or speculation, but rather a confident assertion about a future event.
You can verify these expressions by referring to reliable American English grammar sources or consulting with native speakers of American English for further confirmation.