Thanks for your interest!
In the law, they are very similar. An opinion is somebody's subjective position on an issue. You cannot be sued in defamation for having an opinion, because you are not stating fact. Being judgmental is essentially the same thing; it is your opinion about someone. Your judgment about someone may be based on fact, but your opinion may be as well. Without stating the supportive fact, they remain the same thing, subjective opinion.However, more generally, someone is apt to say it is "just their opinion" because it is just the way they feel, whereas in usage, one is much more likely to say I have a judgment about that person and it is based upon the following facts.
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In the legal world, an "opinion" more often than not is referred to for the writing of a Judge explaining his/her holding or decision in a legal proceeding. For example, a Judge could say I find "this" or "that", or I hold "this" or "that" and then write an explanation (for lack of a better reference) as to why or how that holding or decision was come to. A "Judment" is technically the Order or directive of a court on a legal matter or issue before it, ie- a Judgment of Divorce; a Judgment that defendant owes plaintiff X dollars, etc. It is the paper upon which a legal dispute can often be considered finally resolved (one way or another). The term "opinion" is also used in the law of Defamation, to distinguish between a statement of fact, which might b actionable to sue upon if other requirements are met, and a person's personal "views" on something or someone, which may not be actionable. In the real world, we all have opinions, and everyone who doesn't like our opinion will call us "judgmental"; ah, the vagueries of the English language, if not the human psyche. Now, if you want more, you should consider signing up for a philosophy course.
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