The importance of evidence

Over the years, I've watched many debates between theologians and atheists. I've engaged believers in countless discussions, both in person and online. As I look back on all these discussions, I've come to believe that much of the reason for the continued impasse and, often, frustration on both sides is that prior to the discussion, we aren't really clear on the terms of the discussion. Academics spend hours debating the existence of God without first defining what they mean when they say "God"; and they battle over claims of evidence without first agreeing on the role of evidence in the acquisition of knowledge.

If I had to sum up the argument of modern atheists in one fell swoop, it would be, "there is no evidence for a god or gods." Theists will usually attempt to counter by proffering what they believe to be evidence, but what is too often lost is what really counts as good evidence, and what the value of evidence actually is. Because that central argument of atheism isn't just a claim that must be defended on its own terms – it's also operating on the belief that when it comes to acquiring knowledge about the world, evidence is what really counts. Faith, we argue, is not a valid way of attaining knowledge. That's important, because theists often make the claim that in the end, faith is what counts. They may even take it a step further and assert that all knowledge, including scientific knowledge, is at some level founded on faith. So in this post, I want to clarify the terms and explain why I think theists are wrong.

Good evidence

When we use the term "evidence", it is my presumption that we are talking about scientific evidence – or, more broadly, empirical evidence. I prefer to stick to the term "empirical" simply because the definition of science often varies from one thinker to the next, and it's too easy for theologians to adopt the most narrow definition of science possible and then accuse atheists of "scientism". But we all agree that science is founded upon the philosophy of empiricism. From Wikipedia:
Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily from sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence, especially sensory perception, in the formation of ideas, over the notion of innate ideas or traditions.
Empiricism in the philosophy of science emphasizes evidence, especially as discovered in experiments. It is a fundamental part of the scientific method that all hypotheses and theories must be tested against observations of the natural world rather than resting solely on a priori reasoning, intuition, or revelation. 
A theologian may proffer some other type of evidence, like the last three above – a priori reasoning, intuition, or revelation. In an old blog post, for example, I made the argument that nobody has direct, objective access to the mind of God. Someone replied to the post claiming that God had personally spoken to them, and that counted as "direct" access to the mind of God. But that sort of claim can't really count as evidence because, while it may be evidence to that person, it's not evidence that is equally accessible to all people.

Theists will often claim that they experienced the presence of a god or spirit, and that if we pray or meditate (or whatever), we can also experience this "evidence" for ourselves. But this fails because to experience this evidence requires us to make an a priori assumption about the god or spirit with whom we are attempting to communicate; in other words, we can't pray to a god we do not believe in. Just as a Christian can't pray to Vishnu or Thor since they do not accept the existence of these gods, atheists cannot pray to Jesus in the hopes of experiencing the proper evidence for his existence. This brings me to my first contention:

Valid evidence must be equally accessible to all people, regardless of their a priori beliefs. The only form of evidence which satisfies this criteria is empirical evidence. 


The implication of my first contention is that faith and evidence are two different things – that is, "faith" is not a form of evidence at all, but a claim that we can access knowledge through a distinct epistemology. As long as a theologian and an atheist are debating the merits of evidential claims, they are on equal footing. But when a theologian makes a claim of, for example, revelatory evidence – such as when Ian Hutchinson claimed, in the recent debate with Sean Carroll and Michael Shermer, that he had personally witnessed miracles – they are stepping outside the boundaries of empirical evidence and making a claim that truly amounts to little more than, "I know what I know – so there." It may be convincing to the one making the claim, but it's rationally indefensible. The "evidence" in that case is accessible only to Hutchinson; and since it's not equally accessible to everyone, it's not really evidence at all.

Theists and atheists do generally agree on the importance of evidence, and we all agree that empirical evidence gives us a great deal of information about the world. But theists strongly desire faith to be a cornerstone of their knowledge, so they will often argue that the philosophical foundations of empiricism are themselves based upon faith. In other words, they believe that if they can establish an equivalency between an evidence-based worldview and a faith-based worldview, they will have successfully undermined the foundational pillar of the atheist's claim that faith is not a valid means of acquiring knowledge. 

You may have heard these types of arguments before:
  • The notion that the universe can be rationally understood is based on faith
  • The laws of logic and mathematics are based on assumptions that cannot be proved or disproved – just like faith
  • Empiricism, to the exclusion of faith, is self-defeating – after all, it would be circular reasoning to assert that empiricism can be proved through the use of empirical evidence

These types of arguments may be superficially persuasive, but a little critical thinking reveals them to be irreparably flawed.

Foundations of knowledge (with a hat tip to Evid3nc3)

Empiricism requires us to make to two foundational assumptions:
  1. I exist
  2. My senses generally provide me with reliable information
These are necessary provisional assumptions. The mantra of Rationalism, famously espoused by Rene Descartes, is "I think, therefor I am". But this statement requires the assumption that "I" exist, and that I am able to perceive myself as a rational agent. If we adopt a sort of epistemic nihilism, we might say that our senses are never reliable – maybe my whole life is the dream of an elephant, or an illusion of The Matrix. But such a view essentially says that knowledge does not really exist, so there's nowhere to go from there.

The fact that we can rationally understand the universe is not an assumption, and it's not based on faith – it's an observation buttressed by our ability to make falsifiable predictions about reality, the reliability of which is drawn from abstractions of the reality we observe, like mathematics and logic.

How mathematics is based upon empirical evidence

A mathematical proof may not directly be abstracted from our sensory experience. But set theory, which describes the foundation of all mathematics, most certainly is. Look around your room. Notice that you are surrounded by discrete objects that can be grouped into numbered sets. They may be sets of the same things, or arbitrarily grouped into categories, like "food", "plants and animals", and "man-made things". But we can abstract the existence of numbered sets from the reality that we observe. Imagine, by contrast, if our universe looked like this:

Now, this isn't a perfect example, because being that we are pattern-seeking creatures who inhabit a world full of discrete objects, we will naturally try to impose certain patterns and sets upon this picture. But if we inhabited a world like this, in which there were no discrete objects, then we would not be able to abstract the existence of numbered sets, and we could not extrapolate addition, subtraction, multiplication, and division of sets. All mathematical proofs are ultimately rooted in our evidential experience of abstracting numbered sets into basic arithmetic – thus, in a world like this, there would be no mathematics at all.

The "laws" of logic – or, imagine if we were quantum-sized

In the quantum universe of subatomic particles, strange things happen. Or at least we think they are strange because they do not follow the same "rules" as our macro-world. For example, a foundational law of logic is the law of non-contradiction: that two contradictory statements cannot both be true (A is B, and A is not B). In the macro world, an object is either in one place or another. It takes only one path from one point to another. It cannot be two things at once. But at the quantum level, these apparent contradictions don't apply. A particle can be two places at once; it can be both a point and a wave at the same time. It does not take one path from A to B, but all possible paths simultaneously.

Quantum mechanics is one of the most rigorously developed fields of science in history. It can make predictions with stunning precision. And yet its development illustrates that what we consider the "laws" of logic are not really "laws" at all, but simply abstractions of our sensory experience that are reliable in one particular frame of reference. We let go of an object, it falls to the ground: cause, then effect – A, therefor B. Cause and effect is so pervasive in our daily experience, so absolutely encompassing of everything we do and so unwaveringly predictable that it's easy to take for granted that it is in fact based upon evidential experience. We need only watch an infant's reaction of utter fascination to a yo-yo, and the counter-intuitive action that the the ball does not continue falling but reverses direction, to see that our brains develop a working framework of reality by abstracting our sensory observations into a set of reliable rules. But in the quantum world, cause and effect do not adequately describe what we observe. Virtual particles, nuclear decay, and quantum entanglement all defy our classic notions of A, therefor B – but we must still accept the reality of these phenomena.

Faith is not knowledge

It's easy to see, then, that it's a false equivalency to compare religious faith with a philosophy of empiricism. And the question that those who make claims to a faith-based epistemology must answer is this: how do you know what you claim to know? As long as the answer is "because of the evidence", we can have a rational discussion about the empirical evidence that is equally available to all. But as soon as appeals are made to faith, revelation, intuition, and a priori assumptions, the discussion reaches an impasse. The theist has undermined our ability to fairly and objectively weigh the merits of all available evidence, and implied that their own subjective experience – which may be prone to a litany of cognitive errors and biases – ought to be sufficient to persuade us to adopt their beliefs. Faith, being divorced from evidence, is not and cannot be knowledge, but is rather belief despite the absence of knowledge. It should be clear now why we atheists find that to be unpersuasive.


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