What's the correct usage of the word "Opinion"?

Solution 1:

I suspect we need more context in order to know what the person was reacting to. While the particular sentence seems grammatically correct, there is a difference between "I think" and "in my opinion."

• "I think" means you believe the thing to be true. You can say this about provable/disprovable facts. For example, you can say "I think that tree is 100 feet tall," even though you could just measure the height of tree and figure it out for sure. It just means you're making a guess, and you might be right or wrong.

• "In my opinion" is better used when expressing preference for subjective things. "In my opinion, Michelangelo is a better artist than Da Vinci," is an example of a correct use. For an example of a strange use: "In my opinion, spinach has more vitamin C per serving than oranges." Since you can measure the vitamin C in these foods, you can't really have an opinion about them.