Appeal to common sense

An appeal to common sense is a logical fallacy that occurs when something is claimed to be true because (according to the speaker) it is "common sense" or "obvious" that the claim is true. It is a form of or similar to an Argument from incredulity. It's also an emotional appeal and an informal fallacy.

Form
P1: X is obvious.

P2: (unstated) Anything obvious is true.

C: X is true.

P1: X is common sense.

P2: (unstated) Anything that's common sense is true.

C: X is true.

Examples
"It's obvious that the world must have a creator!" or "Obviously, just like a watch has a maker, the world does!"

(Argument from incredulity) "It's obvious the world has no creator!" (which is the opposite of the above example)

"It's obvious that the Earth is flat!"

"It's just common sense to give both sides a platform to peacefully debate on."

Problems
Different people have different and sometimes contradictory "common sense"; there is no universal common sense. Even if everybody alive agreed on something being common sense, it wouldn't automatically be true. This is especially evident in the case of politics, "common sense" might be defined as whatever is politically tolerated, which would also be an appeal to authority. For example, discrimination against gay people may be seen as "common sense"; however, it's not morally justified — it's homophobia. This fallacy could also be used to argue against advancements in gay rights because "it's just common sense to dislike homosexuality". Moreover, political ideologies greatly affect our perception concerning "common sense". Conservatives may hold a notion of common sense that's quite different than the common sense held by other political ideologies.

There is a certain uniqueness to this fallacy. The appeal to common sense fallacy doesn't completely rely upon appealing to tradition and popularity because it states something is true due to an opaque "common knowledge" or "self-evident fact", regardless of the evidence suggesting otherwise. The "obviousness" may simply be whatever we perceive as fact from experience without any critical thinking and skepticism, or whatever we "automatically know without having to learn". For instance, you may have thought you once saw a ghost, therefore, you could argue that it's common sense to believe in ghosts since you supposedly experienced a ghost sighting. With this fallacy, a conclusion can be made without evidence, testing, analyzing, researching, logic, or reasoning — which means it fails to utilize the scientific method.

Without the scientific method, "common sense" can be utter pseudoscience. Flat earth was once widely believed to be true — so was geocentrism. However, people surmised that these theories were factual without using the scientific method, yet they were reckoned to be legitimate — therefore, were common sense. As science advanced, both geocentrism and flat earth eventually were acknowledged as pseudoastronomy, but had science embraced the appeal to common sense fallacy, how would we have accepted oblate spheroid earth and heliocentrism? Scientists would have continued perpetuating flat earth and geocentrism because "it's just common sense to believe in these theories" or "it's obvious the world is flat, and that the solar system orbits around it".