The logic of belief: How do we know what’s true?

At first glance, philosophy and science might seem worlds apart – one grounded in careful reasoning, the other in measurable experiments. But for Iowa State Associate Professor of Philosophy Stephen Biggs, both disciplines are driven by a shared goal: figuring out what’s true.

Belief in bundles

Biggs studies epistemology – the branch of philosophy focused on the nature of knowledge – and much of his work focuses on abduction, also known as “inference to the best explanation.”

Abduction is the form of reasoning we use when we say, “This is probably true because it best explains the facts we have.” Biggs investigates what makes some beliefs more reasonable than others and where this kind of reasoning might fall short.

“If you want to believe something like ‘it’s 80 degrees outside,’ you have to believe in temperature, and in tools that can measure it,” Biggs said. “Beliefs come in packages. If you accept one, you’re usually committing to a bunch of others, too.”

Biggs’ research centers on tracing the ripple effect of our beliefs, and how one commitment often leads to others. He sees philosophy as evaluating “packages” of beliefs, determining which ones connect coherently, and which ones create contradictions.

“You’re trying to find the most rational overall set of beliefs,” he said. “What’s the best model that maps onto reality?”

For Biggs, philosophy is about evaluating which packages of belief make the most sense given the evidence, and sometimes that means letting go of ideas you thought were solid.

“Sometimes you’ll hit on that next implication and realize, ‘Oh no, I don’t want to believe that,’ which means I have to go back and rethink something else I believed earlier.”

Why philosophy needs reasoning

Biggs sees philosophy as connected to the sciences. Like scientists, philosophers must grapple with uncertainty, conflicting evidence, and competing theories. But instead of running physical experiments, they rely on structured arguments and thought experiments.

“When an experiment contradicts a theory, scientists don’t always reject the theory right away,” Biggs said. “They question the experiment first – Was the setup flawed? Did something go wrong?”

Biggs argues this kind of thinking is essential to science itself. He points to Albert Einstein’s reasoning about the nature of motion and time, which began as a philosophical reflection before being formalized mathematically.

“Before Einstein sat down and did math, he was doing theoretical physics, which is basically philosophy,” Biggs said. “In simple terms, he was just reasoning in a good way and coming to reasonable conclusions.

A paper on justifying beliefs

Biggs’s upcoming paper addresses the question: Should inference to the best explanation have the final say when justifying beliefs, or is there some better procedure?

Bigg’s answer is subtle and the writing process, he admits, is often reflective. He begins by mentally working out an argument, but the writing process sometimes reveals flaws he hadn’t initially considered. This prompts a revision in logic and adjusting the premises.

“I’ll find things that challenge my view, and I try to respond to them. Sometimes that means adjusting my argument, sometimes it just means preparing to defend it,” Biggs said.

Eventually, he brings in scholarship, reading other philosophers to see who has considered similar problems and how his work fits into the conversation.

Biggs has not faced much pushback on his papers, as he says they rarely draw intense backlash, but he welcomes it.

Why this kind of thinking matters

While Biggs’s work is theoretical, it touches on questions that affect everyday life. How do we know which beliefs are reasonable? What happens when a belief leads to an uncomfortable conclusion? What do we do when our beliefs conflict?

“I don’t think there is any simple procedure that tells you which package of beliefs is best. You’re weighing a bunch of imperfect criteria. It’s kind of messy, all things consider reasoning,” Biggs said.

For students used to a lab setting, philosophy might feel disorienting, like experimenting without equipment. But Biggs argues the core skill is the same: testing, questioning, refining.

“You’re being your own critic,” Biggs said. “You’re thinking about how even a small change in belief might push your thinking in a totally different direction.”