Overview
“A priori” refers to knowledge or justifications that exist prior to experience or empirical evidence, generally achieved through deductive reasoning.
Those who argue that some knowledge is a priori point to mathematics and logic. If two people were raised in completely empty rooms, incapable of any experience outside of their mind’s wonderings, both could arrive at the same logical conclusions. If a = b and b = c, a = c. Often, those arguing for the existence of a priori knowledge come from philosophical traditions developed by rationalists or idealists. Immanuel Kant is perhaps the most famous figure associated with developing this concept.
Others argue that no knowledge is a priori, a camp sometimes called radical empiricism. John Stuart Mill argued that even math and logic are systems built from empirical observations first. If the universe suddenly changed so that when four equivalent objects are grouped together, they disappear, we would start saying 2 + 2 = 0. In that case, 2 + 2 = 4 was never a fact we knew, just a generalization that was very strongly confirmed.
Quantum physics as a field has begun to challenge long-standing assumptions that logical rules as we’ve been able to derive them are universally true. Those like Willard Van Orman Quine have proposed models of human knowledge that function more like a web where knowledge in the center is difficult to change as it would disrupt the entire system, and the rules of quantum mechanics make it so that basic laws we took for granted are at least questionable.
For instance, with the Heisenberg Uncertainty Principle, we cannot know both where a particle is or how fast a particle is going. This means if A is a claim about the particle’s location, and B and C are claims about the particle’s speed, we cannot know A AND B or A AND C. This means we run into a problem with the distributive law. Normally, we would say A AND (B OR C) should be equivalent to (A AND B) OR (A AND C). However, with the Uncertainty Principle, the first is True while the second is False. There are some arguments about fixing this without changing our known rules of logic, but it’s likely we won’t have a resolution to this debate for a while.
According to the 2020 PhilPapers Survey that reached out to 1,800 academic philosophers, about 72.8% at least lean towards the existence of a priori knowledge. About 18.5% at least reject its existence or lean towards pure empiricism. About 8.7% are either undecided or have an alternative view.
History and Etymology
“A Priori” is a Latin phrase that translates to “from what comes before.”
In the past, philosophers like Descartes argued that God implanted ideas into our minds the moment as part of our birth. Plato theorized that our souls remember truths from past lives. A priori referred to our ability to make inferences about cause-and-effect; for instance, if you know your house caught on fire, you might reason that it will quickly turn to ashes if left alone.
When the concept of a priori knowledge was reinterpreted by Kant, he defined it as having truths independent of sensory experiences. He argued you don’t have to check whether 2 + 2 = 4 for every single pair of pairs in the entire universe. You can use reason alone to know 2 + 2 = 4.
Commentary
In neuroscience, a common paradigm to understand the brain is to see it as a prediction engine that is constantly making assumptions about the world independent of experience in order to help navigate it. “I am inherently a broken human” is a claim to a priori knowledge. “My Higher Power will cure me of my defects if sough” is another. “An abstinent life is the only one worth pursuing” is yet another. Claims to a priori knowledge can be found in every aspect of life, and that includes mental health and recovery. Our brains often begin with these a priori assumptions when processing information about the world, which means we can easily have a tendency to interpret new information so that it aligns with those assumptions.