Welcome back to The Philosopher’s Lexicon. My primary goal in this series is to explore common philosophical vocabulary, hopefully transforming these words from useless jargon into meaningful terms. My secondary goal is to highlight how contentious some of these terms can be – especially those which seem obvious. These definitions will not be comprehensive by any means, so please feel free to add your own understanding of each term as we go.
This week’s entry into the Philosopher’s Lexicon will once again explore a distinction rather than a solitary term: the difference between logical possibility and causal possibility, a distinction which comes to me from Kant, quite generally, and Nils Ch. Rauhut’s Ultimate Questions, more specifically. What I find most interesting about Rauhut’s take is his shift away from the more common, yet slightly intimidating conversation about logical and causal necessity to the more open realm of possibility.
Like the difference between statements made de dicto and statements made de re, and between ontology and epistemology, the difference between logical and causal possibility is key to understanding, analyzing, and evaluating a philosophical theory. Understanding this distinction is also important when crafting theories and – especially – thought experiments and predictive models not just in philosophy, but in mathematics, the hard sciences, and the social sciences as well.
When we decide whether or not something could happen, we are typically speaking in terms of causal possibility. Causal possibility – and not “casual” possibility (as it is often mis-written) – refers to things that could happen in the world, given its present state. That means we have to take into consideration not just the laws of logic, but the laws of physics, the current circumstances, the available resources, and more.
One of the conditions of causal possibility is logical possibility. In order for a proposed scenario to be logically possible, you have to be able to imagine the proposal – either in literal images, or in symbolic representation (i.e., math, words, or formal language) – without experiencing any internal contradiction. The proposal doesn’t have to be physically possible, or likely to happen, but merely logically imaginable. To wit: for a proposal to be causally possible, it must be logically possible, but logical possibility has no requirement of causal possibility.
For example, the statement “Without the aid of technology, a man can fly to the moon” may not be causally possible (due to the physical limits of human beings and the distance to the moon, among other things), but it is logically possible. It’s easy to imagine, even picture. In Ultimate Questions, Rauhut offers a helpful rule of thumb for determining logical possibility: if you could picture the proposal happening in your mind, it is logically possible. In truth, you may need to elaborately track premises or do complex equations to “draw” the picture, but the principle stands.
On the other hand, the statement “Without the aid of technology, a man can walk ten miles” is both logically possible – easy to picture without experiencing an internal contradiction – and causally possible – humans are fully capable of walking ten miles.
Finally, the statement “Bill is both physically taller and shorter than Sam” is both logically – and thus causally – impossible. It cannot be imagined or depicted even in the most logically isolated circumstances, and thus could never causally happen.
In short, when crafting or assessing whether a proposition is realistic, it’s important to take stock of what kind of possibility you are intending to establish. If we mix up our categories, we’ll likely reject useful logical propositions because they’re causally outlandish, and fear unlikely causal scenarios because they make logical sense.