1. He finished the project for five days.

2. He has finished the project for five days.
3. He read the book for five days.
4. He has read the book for five days.
[Are the four sentences all grammatical?}

5. He read the book in five days.
6. He finished reading the book in five days.
[What is the difference between #4 and #5? Does #5 mean #6?]

The difference between #4 and #5 is that #4, he read the book for five days, meaning that he could have started reading the book and five days later, he stopped reading and he didn't finish it. And #5 he finished it within 5 days. Does that make sense? And yes, #5 and #6 mean the same.

Also, #1 and #2 don't make sense.

chicken is right. Did you read the definition of the world "for' that I posted for you? What do you not understand?

1. The sentence "He finished the project for five days" is not grammatically correct. It should be corrected to "He finished the project in five days" or "It took him five days to finish the project."

2. The sentence "He has finished the project for five days" is also not grammatically correct. It should be corrected to "He has finished the project in five days" or "It has taken him five days to finish the project."

3. The sentence "He read the book for five days" is grammatically correct. It means that he spent a continuous period of five days reading the book.

4. The sentence "He has read the book for five days" is grammatically correct. It implies that he started reading the book five days ago and has been reading it continuously since then.

5. The sentence "He read the book in five days" is grammatically correct. It means that it took him five days to complete reading the book.

6. The sentence "He finished reading the book in five days" is grammatically correct. It has a similar meaning to sentence #5, suggesting that it took him five days to complete the reading of the book.

There is a difference in meaning between sentence #4 and sentence #5. Sentence #4 implies that he has been reading the book continuously for the past five days, while sentence #5 simply states that it took him five days to finish reading the book.

Sentence #5 does not necessarily imply the exact same meaning as sentence #6. It solely states the period of time taken to complete the reading, whereas sentence #6 could suggest the completion of reading the book along with other activities or tasks.