According to the Little, Brown Handbook by Fowler and Aaron, an opinion is "A conclusion based on facts; an arguable, potentially changeable claim" (876). What this means is an opinion
has closely examined factual evidence that it can rely upon to support it,
can be disagreed with because it relies on different interpretations of evidence, and
is open to being changed because it is not known with absolute certainty (Fowler and Aaron 188).
Opinions are important because they are the foundation of most academic essays. For example, in argumentative essays in particular, your thesis and claims must be statements of opinion; otherwise, the essay is not an argument because no one can effectively disagree with it. If you struggle with how to phrase opinions, try one of two reliable methods:
Judgmental Adjectives: using this method, you express your opinion through an adjective that passes judgment on something. For example, in the sentence "That solution is irrelevant because it doesn't apply to this situation," the adjective irrelevant expresses judgment that another person could disagree with, based on whatever evidence is presented.
Policy verbs: this method uses particular verbs that express the way a person thinks the world should be or things should be done, which is something others can dispute based on presented evidence. Verbs that fit this category are ones like should, ought to, must, and need to. For example, in the sentence "People should recycle because it reduces plastic waste in the ocean," the word should expresses one of their ideals that you might contest.
Source information
Fowler, Ramsey, and Jane Aaron. The Little, Brown Handbook. 2nd ed. for Tulsa Community College, Pearson, 2012.