Given a positive ontological claim X, is not-X the default position?

Question

Given a positive ontological claim X, I see at least four different subjective positions one could adopt regarding X:

• I believe that the evidence provides persuasive reason to believe that X is true ("X-ism")
• I believe that the evidence provides persuasive reason to believe that X is false ("a-X-ism")
• I believe that the evidence does not provide persuasive reason to adopt one conclusion or the other ("X agnosticism")
• I don't care ("X apathy")

Examples of positive ontological claims:

• X = "Alien civilizations exist"
• X = "We live in a multiverse"
• X = "There is an even number of atoms in the universe"
• X = "There is an odd number of atoms in the universe"
• X = "There is a flying teapot between Earth and Mars"
• X = "Bigfoot exists"
• X = "Ghosts exist"
• X = "God exists"
• X = "China plans to invade the US"
• etc.

When faced with a positive ontological claim X, what should our default position be?
X-ism, a-X-ism, X agnosticism, X apathy or something else?

Is assuming not-X ("a-X-ism") the most rational position to hold by default in the absence of compelling evidence for X?

Does the answer depend on the claim X, and if so, how and why?

Answer 1

Generally speaking, yes, disbelieving an object is the more reasonable course of action if there isn't any evidence for it. With a caveat.

The caveat is that to say you disbelieve in the object is really being a bit imprecise. It would be more precise to speak about your degree of belief in the object, which might be represented by a number between 0 and 1. Without evidence for the object, your degree of belief would be fairly low, but never exactly 0. We say you disbelieve in the object when your degree of belief is "sufficiently close" to 0, below some unspecified threshold, such as 0.1.

The degree of belief should be nonzero because you should always admit that yes, maybe there is such an object. You just don't think it is likely.

To justify why you don't think it is likely, we can mention Occam's razor. Another way to think about it is that to say an object exists is really to express a conjunction of many propositions, and the more propositions you put in conjunction the lower the probability of the conjunction is. For instance, consider the claim that there is a carved figurine of an owl on my desk. This is really a conjunction: there is a figurine AND the figurine is of an owl AND the figurine is small enough to sit on a desk AND the figurine is on my desk AND the figurine was carved from wood. Each additional condition makes the overall sentence less likely.

Of course, with all the example sentences you listed, there is a lot of evidence to consider for and against. So we can base our estimation of those sentences on more than just this "default."

Answer 2

First, I disagree with your categorization entirely. One could not-know and not-care; one could not-know, not-care, and not-believe; one could know, not-believe, and not-care; one could care, not-know, and believe. One could think something is likely but be uncertain. The positions you've laid out do not exclude one another and are too absolute, and therefore I reject your framework entirely.

For example, I believe it is likely that there is, somewhere in the universe, another planet that has intelligent beings on it. It's a big universe, there are lots of planets, life is possible, intelligence is possible, etc. However, we have no positive proof that such is the case. So you will get different answers from me about extra-terrestrial intelligence, depending on how you phrase the question. Do I believe it is possible? I'm almost certain it is possible. Do I believe it is true? I think it is likely to be true. Do I know if it is true? I do not.

So on this claim, I accept X as likely, but I don't hold X as definitively true. As @causitive states in their answer, there are degrees of belief.

The second part of your framework I reject is the idea that there is a single "default" position. There are any number of default positions. One could decide that they believe anything that some authority says, for example, and take that as their default.

My own default position is that, given a novel proposition, I judge how likely that proposition is based on my current state of knowledge, my assessment of the source, and my assessment of any new information that is brought to my attention.

Which of these defaults is better really depends on what your goals are. If your goal is to have an internal mental model that is as consistent with observed reality as it can be, accepting propositions uncritically on faith seems like a poor default. But if your goal is to continue to live harmoniously in a community that will kick you out and shun you if you question the authority, it's a serviceable default.