Necessity and Contingency:
It’s common to think that the world could have been different from the way it actually is. Maybe someone who decided to have toast for breakfast could have decided to have cereal instead. Maybe the Axis powers could have won World War II instead of the Allies. Or maybe a childless couple in the actual world could have produced children.
These are all examples of contingent events or beings. They are part of possible worlds that can fail to be part of the actual world. Most ordinary objects are contingent: clouds, rocks, cars, animals, people. Even if they exist, it is possible that they didn’t exist.
In contrast are necessary objects. These are things which are part of all possible worlds. One example which many philosophers consider necessary are truths about mathematics. It is true that there is no even integer between 2 and 4, and it’s a truth which holds in all possible worlds. Even in a fantasy world where magic, dragons, and unicorns exist, this fact would be true.
One way to understand the range of possibilities is to categorize four different ways things can be possible. One is physical possibility. These are the range of things which are possible if the laws of physics hold true. For example, according to relativity, it is impossible for anything to travel faster than the speed of light. So, all physically possible vehicles and communication devices will travel or transmit data at or below the speed of light.
The second category is broader than physical possibility. This is metaphysical possibility. Metaphysical truths are taken to hold in all possible worlds, but their negations don’t lead to logical contradictions. Take the concept of morality, many philosophers believe that if moral truths are objective, then they are necessarily true. It is true, for example, that torturing babies for fun is wrong in all possible worlds. Even in a world with different physical laws, such as gravity not existing, this moral fact would hold true. The negation of this moral statement “Torturing babies for fun is not objectively wrong” is not a logical contradiction, it doesn’t defy a law of logic such as the law of noncontradiction or the law of excluded middle.
The third category is logical possibility. These are all possibilities which don’t defy the laws of logic. “Bob is alive and not alive” is a logical contradiction as it defies the law of noncontradiction. “The year 2000 is not the year 2000” would defy the law of identity. And a third possibility besides an object being either a rock or not a rock would defy the law of excluded middle. These are the laws of classical logic, although there is debate about whether there can be other logics and whether these laws are universally true.
Fourth is epistemic possibility. This is the broadest category, and it is what is possible given what a person knows. An individual may know the axioms of Euclidean geometry, but not be aware of all that must logically follow from those axioms. For a beginner in geometry, it may be epistemically possible that the Pythagorean theorem is false. Current unsolved questions in mathematics also fall into this category, since for all we know, Goldbach’s conjecture could be true or false given, but its truth value must logically follow from the axioms of number theory.
These types of possibility can help refine our ideas about what exists and can exist. Take the concept of God, which has occupied Western thinkers for millennia. Many religious scholars believe God is omnipotent, and a standard way to understand omnipotence is that he can do anything that doesn’t logically contradict itself. He can defy the laws of physics, create miracles, but not create an even integer between 2 and 4. Given these limitations, interesting questions arise such as whether he can alter the past or create a world in which humans freely choose to worship him.
Is it logically possible to alter the past after it has already occurred?
Is it possible to guarantee that a free choice leads to a specific outcome?
God is also believed to be a necessary being who exists in all possible worlds and is the cause of all contingent objects such as stars, planets, life, and people. This is the result of a line of thinking which generally states that contingent objects require an explanation for their existence, but that a necessary being either doesn’t require an explanation or provides its own from the impossibility of its nonexistence. Nontheistic philosophers tend to claim that the world originated from a contingent cause, or posit a necessary non-theistic cause. Questions on the origin of the universe will require addressing the contingent aspects of the world and whether or not they need explanations or causes.
Possibilities also play a role in the fine-tuning argument. Proponents argue for the existence of God by beginning with the fact that it is unlikely that the laws of physics would permit the existence of life given our best understanding of those laws and the way the universe would have been if they were adjusted even slightly. According to the argument, the best explanation for how the universe has laws which permit life is that a being adjusted those laws out of all possibilities to permit for life, presumably an all-powerful, loving God. However, if a multiverse with different regions of space-time with different physical laws has a significant probability of existing, that complicates the argument. There would then be no need to assert the existence of a fine tuner, as all possibilities of laws actually exist in different universes.
In contrast to the ordinary beliefs of the contingency of physical objects or physical laws is the idea that all things are necessary. There is only one possible world: the actual world. This is the thesis of necessitarianism, one famous proponent of which was Baruch Spinoza. This is very counterintuitive, as it states that it’s impossible for even trivial events such as a choice of breakfast to have been otherwise. The main argument against this relies on conceivability. As an example, there are no contradictions in someone choosing cereal instead of toast one day, even if they actually happened to eat toast that day. Although the question arises, is this enough to show that necessitarianism is false?
The possibility of certain concepts is also used in other arguments. P-zombies are one example. A p-zombie is physically identical to a human, but it doesn’t have conscious experience. It responds to physical stimuli just as a human would with no subjective point of view. If such a creature is logically or metaphysically possible, this would show that consciousness is not identical to some physical object or process, and that therefore consciousness is not physical. However, even if it is epistemically possible, its possibility in other respects is questioned.
Moral argumentation also involves the analysis of possibilities. According to modern science, objects on the human scale are either completely or nearly completely deterministic. This means that only one outcome can follow from a previous state of the universe, or that if other outcomes are possible, they are highly improbable.
However, if it is physically impossible for a particular human to avoid committing an immoral action, in what sense can we hold him or her responsible for it? It may have been an inevitable result of the Big Bang that Jack the Ripper murdered prostitutes and mutilated their corpses, just as it’s inevitable for an unsupported rock to fall to the ground. If he can be held culpable for those physically unavoidable actions, what does the concept of moral culpability consist of?
According to compatibilists, the correct conclusion is that a person can be morally culpable even for physically inevitable actions if that action resulted from that person’s desires and reasoning. And of course, incompatibilists disagree.
Since moral philosophers who believe in objective morality also tend to hold moral facts to hold true in all possible worlds, unusual thought experiments can still be a useful form of discussion in moral philosophy. Utility monsters are creatures which feel many times more pain and pleasure than ordinary individuals, and may not even be biologically possible, but they can still be an argument against utilitarianism. People seeds are hypothetical pollen-like objects which can grow into fully formed humans, and the concept can be a useful argument in abortion debates and falsifying the principles that anti-abortion individuals claim to hold.
There are many more interesting discussions of possibility, such as what possible worlds even are or how to understand potential objects, which are merely possible and not actual. However, as a starting point, this has mostly been an examination of possible or impossible objects and what their implications are.
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