An opinion is an idea that is based more on how a person feels, and it may or may not be based on factual information. For example, someone might say, "I really dislike Compsognathus" (Fig. 2.4). When asked why, the person might say, "Because someone told me that it was a scavenger and I don't like scavengers." In this instance, what this person has expressed is an opinion. A listener has few ways of knowing what evidence or rationale supports that feeling, as well as the subsequent statement. Opinions are not necessarily incorrect and may actually coincide with factual information, but they are not derived scientifically. Thus, a flippant rejection of an evidence-based hypothesis or theory as "just an opinion" is fundamentally incorrect. The dismissal itself is an opinion because it has no expressed factual information supporting it and was not formed through evidence-based reasoning.
John Bell Hatcher, a dinosaur paleontologist (Chapter 3), expressed a similar perception about the relative value of opinions in a 1907 publication, where he wrote about the errors made by two other paleontologists regarding the identification of some ceratopsian dinosaur remains (Chapter 13):
They [the errors] are, moreover, striking examples of that axiom so often disregarded in vertebrate paleontology, namely, that one observed fact is worth any amount of expert opinion.
Hatcher's thought also relates well to the use of single or personal observations and their value in science. Anecdotes, which are personal-experience stories communicated by one person to another, are not considered scientific, especially if they are related as second-hand information. The use of anecdotes to support a hypothesis risks the possibility of an individual fallacy, which means that a single observation by one person is applied universally in a potentially incorrect way. For example, someone might say, "I have a friend who discovered a new species of dinosaur, therefore anyone can discover one." Because not all people have the right geographic location, training, skills, funding, or luck to find a dinosaur within their lifetimes, let alone a new species, such an assertion can be easily disproved. Just because a circumstance is possible does not mean it is probable, nor does it mean that it actually happened or will happen.
Argument by authority is another method that uses the views of an "expert" associated with a scientific discipline to support what may turn out to be mere opinion. In this case, an authority, such as someone who may have numerous degrees from well-known universities, might be quoted in a way that shows that person's support for a particular idea. For example:
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