In Citations and Your Credibility, construction site expert witness William Gulya, Jr., President & CEO, Middlesex Trenching Company writes:
If you are stating a fact or opinion, always check and cite your reference and source correctly. The common definition of fact vs. opinion is: Facts are objective, i.e., they can be proven. A fact is something that can be verified and backed up with evidence. Opinions are subjective, i.e., they express a preference or bias. An opinion is based on a belief or view. It is not based on evidence that can be verified. To check if something is a fact, ask yourself, Can this statement be proved? To check if it is an opinion, ask yourself, “Does this tell a thought or feeling?” “Would the statement be true all of the time?” Look for key clue words such as feel, believe, always, never, none, most, least, best, and worst. Cite your source and references in the proper format, e.g., Harvard, MLA or APA. This will ensure your report is clear, concise and credible. There will be no question as to what is provable fact, your opinion or supporting opinions of others.