An opinion is a personal view or judgment. It is not necessarily based on fact, and it is not necessarily true. Opinions can be informed or uninformed, reasoned or arbitrary, widely shared or idiosyncratic. In everyday speech, opinion is often contrasted with fact. A fact is something that can be verified. An opinion is something that someone believes. But the distinction is not always sharp. Many facts are contested, and many opinions are well-grounded.

Philosophers have analyzed opinion in different ways. Plato distinguished opinion from knowledge. Opinion is changeable and fallible. Knowledge is stable and justified. For Plato, opinion is the middle ground between ignorance and knowledge. It is what we have when we perceive the world of becoming, not the world of Forms. In modern philosophy, opinion is often treated as a belief that is held without certainty. Some philosophers argue that opinion is essential to democracy. A democratic society depends on the free exchange of opinions. Others argue that opinion is a threat to truth, especially when opinions are treated as facts. The tension between opinion and truth is one of the central problems of public life.

Kinds of opinion

• Informed. Based on evidence and reasoning.
• Uninformed. Based on ignorance or prejudice.
• Public. Shared by a group or society.
• Expert. Held by someone with specialized knowledge.

Opinion is not the same as belief, though the two overlap. Belief can be certain. Opinion is usually held with less confidence.