Philosophy is no longer a field conducted entirely from the comfort of an armchair. Over the past decade, this notoriously abstract discipline has developed a branch of “experimental philosophy” that conducts its own scientific studies.

Though such work continues to face resistance from conventional armchair philosophers, there’s an increasing focus on using empirical studies in conjunction with philosophical thinking: One survey found that 62% of highly cited papers from 1960-1999 used a priori (purely reason-based) methods. From 2009 to 2013, just 12% of comparably cited papers used a priori thinking alone.

The majority of these recent studies relied on existing empirical research, while a minority conducted their own original experiments.

Joshua Knobe, philosophy and cognitive science professor at Yale, was one of the first to begin conducting such experiments. He began to do so, he tells Quartz, after a philosopher responded to a paper he’d published in a psychology journal. He was studying for a PhD in philosophy at the time and realized he could use the techniques he learned in the sciences to advance philosophical thinking.

Questioning their assumptions

One of his most famous results, now known as the “Knobe effect,” found that people judge whether or not an action can be considered intentional depending on whether the consequences are good or bad.

Knobe asked people to consider a scenario where a chief executive is told about a new initiative that will increase profit, but hurt the environment. When asked whether the CEO intentionally harmed the environment, the vast majority (82%) said yes. But when the scenario changed, so that the profitable initiative benefits the environment, just 23% said the chief executive had intentionally helped the environment.

These findings suggest that our judgements about whether an action is intentional are affected by whether or not we view the act as moral. Philosophers have long argued that the morality of an action is partly determined by whether or not an act was intentional—as a basic example, someone would likely be judged more negatively for knocking over a vase on purpose rather than by mistake.

But Knobe’s effect shows that the relationship is more complicated, as our understanding of intentionality itself is affected by the moral consequences of the act. Of course, a philosopher might decide that the moral intuitions—instinctive ethical judgements—revealed by the Knobe’s effect aren’t valid, but the experiment gives important insight into how humans judge intentionality.

These philosophical experiments often overlap with studies of psychology. But philosophers use this research into human behavior to test their assumptions about moral truths.

“Using carefully controlled studies and the right statistical methods, you can start to get evidence about some of the unconscious principles we’re applying in trying to figure out whether someone is morally responsible or not,” Chandra Sripada, philosophy and psychiatry professor at the University of Michigan, tells Quartz.

Having collected data about how intuitive judgments are made, philosophers can then reflect on whether these principles are sound.

Tools of the trade

Joshua Greene, philosopher and psychology professor at Harvard University, tells Quartz that such work is necessary for philosopher to “understand the tools they bring to their job.”

“In every philosophical discussion, conclusions turn on intuitions about what’s right or wrong, plausible or implausible, something one would or would not say,” he adds. “Philosophy needs psychological experiments to understand how we’re arriving at our conclusions.”

For example, Greene conducted experiments showing that people react more negatively to the idea of pushing someone to their death in order to save five lives (a variant of the Trolley problem) than hitting a switch to drop someone through a trapdoor.

“You can’t know this by introspection, you have to do an experiment. And when you learn that this is what’s going on your head, you say, ‘Well if that’s what I’m responding to, then maybe I need to rethink that judgment,’” says Greene.

Certain intuitions can be linked to mechanical brain functions, he says, and so it’s important for philosophers to take into account how human and animal minds work.

Though experimental philosophy is growing, those in the field say they face resistance from some armchair philosophers, who can be quick to dismiss their work. Sripada says he finds this strange—armchair philosophy is still valuable, and so why not embrace experimental philosophy as well?

“I also work psychiatric neuroscience,” he says. “When someone says, ‘I’ve got a magnetoencephalograph, I can look at particular signal form the brain’, the other scientist doesn’t say, ‘Shut up, I’ve already got an EEG or fMRI, you have no role to play whatsoever.’ But some philosophers instinctively reason that way.”

A return to “natural philosophy”

In some respects, the principles applied in experimental philosophy have long been evident in the field. Greene points out that what we now call “science” was once “natural philosophy”; Newton was considered a philosopher, while Aristotle was a great naturalist. Knobe adds that Hume’s “Treatise of Human Nature” was subtitled, “being an attempt to introduce the experimental method of reasoning into moral subjects.”

However, it’s certainly the case that the statistical and scientific methods seen in philosophy today are a new development.

Knobe believes that the trend is part of a broader acceptance of these techniques in academia. “Thinking about all sorts of questions seems to have become much more affected by experimental methods,” he adds.

But others believe that the field is gathering pace because, quite simply, it’s an effective way of advancing philosophical ideas.

“The only way to move forward is to gather new information about the world, including the machines in our skulls that we use to make sense of the rest of the world,” says Greene. “The philosophical problems that can be solved from the armchair have already been solved.”