1. Julie could have bought the book.

2. Julie might have bought the book.
3. Julie could have bought the book, (but she borrowed it from the library instead.)
4. Julie could buy the book yesterday.
5. Julie was able to buy the book yesterday.
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Q1) It is sometimes confusing if #1 means #2 or #3? #2 means possibility. #3 means that anyway Julie didn't buy the book. What do you think about that? Does #1 mean #2 or #3?

Q2) #4 means #5, right?

1 and 2 mean about the same thing.

3 is fine if you remove the parentheses. This sentence gives details about what Julie did after she didn't buy the book. The other two don't.

4 and 5 mean about the same thing, but 5 is the better phrasing.

Q1) The statement "Julie could have bought the book" in sentence #1 can have two interpretations:

a) It can mean the same as sentence #2 - that there was a possibility that Julie bought the book. This suggests that Julie had the option to buy the book, but it's uncertain whether she actually did.

b) It can also mean the same as sentence #3 - that Julie had the opportunity to buy the book but decided not to, opting to borrow it from the library instead. This interpretation implies that Julie had the choice to buy the book but ultimately chose not to do so.

Determining the intended meaning relies on the context of the sentence or the surrounding information. Without additional information, it is not possible to determine whether #1 means #2 or #3.

Q2) Sentence #4, "Julie could buy the book yesterday," does not convey the same meaning as sentence #5, "Julie was able to buy the book yesterday."

#4 suggests that Julie had the ability to buy the book on a past day (yesterday), but it does not provide any indication whether she actually did buy it or not. It simply states that she had the potential or capability to make the purchase.

On the other hand, #5 explicitly states that Julie had the ability to buy the book on a specific past day (yesterday) and implies that she did indeed make the purchase.

In summary, #4 does not necessarily mean the same as #5, as #4 only suggests the potential to buy the book without confirming the actual action, whereas #5 confirms both the ability and the action of buying the book.