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How Speaking a Second Language Affects the Way You Think

The role of inhibition in language, thought, and emotion.

Key points

  • It is rare when a bilingual person speaks two languages with native-like fluency. Most still have a dominant language.
  • A study found that people shift from intuitive to rational thinking when they use their second language.
  • Brain imaging research shows that the prefrontal cortex is activated both in second-language use and in rational thought.
Syda Productions/Shutterstock
Source: Syda Productions/Shutterstock

About half of the world’s population uses a second language in their daily lives. Some areas of the world, such as Switzerland and Singapore, are bilingual hotspots where virtually everyone speaks two or more languages. However, even in America’s largest cities, there are sizable populations that speak a language other than English with family and friends.

The naïve view is that a bilingual person is someone who speaks two languages with native-like fluency. However, this kind of “balanced” bilingualism is rare. In the vast majority of cases, bilinguals have a dominant native tongue and a second language they can speak with some effort. These are the kind of bilinguals that Spanish psychologist Albert Costa and his colleagues reported on in a recent article in the journal Current Directions in Psychological Science.

Costa and his colleagues work in Barcelona, another bilingual hotspot where many people speak both Spanish and Catalan. The team was interested in finding out if speaking a second language affected people’s abilities to make decisions. You might think that because speaking a second language is so effortful, their decision-making processes would be impaired. But this isn’t what Costa et al. found.

First, let’s clarify that we’re not talking about how a specific language affects thought processes. Psychologists used to believe that thinking was “nothing more” than speech turned inwards. And since every language carves up the world in a different way, they reasoned, the language you speak constrains the way you think. This idea is known as linguistic determinism, and it has been thoroughly debunked, despite nonsense that still circulates on the Internet, such as “Eskimos have 200 words for snow.” (They don’t.)

Rather, Costa and colleagues were looking at how people make decisions while using their second language — whatever that language may be. So the research question is whether expending the effort of speaking a second language impacts that person’s ability to make good decisions. And the answer to that question is yes, but in unexpected ways.

The researchers considered decision-making in a second language in three domains, specifically judgments about:

  • Losses, gains, and risks.
  • Cause and effect.
  • Moral issues.

We already know a lot about how people make decisions in these realms, so let’s compare these data with performance in a second language.

Losses, gains, and risks. Let’s say I give you $1.00. I then propose we flip a coin. If it comes up heads, you give me the $1.00 back. But if it comes up tails, I’ll give you an additional $1.50, bringing your net gain to $2.50. Will you take the bet? Probably not. Most people prefer the safety of $1.00 over the 50-50 chance of $2.50.

Plenty of research shows that people evaluate losses as greater than gains, in a process known as risk aversion. However, from a mathematical perspective, this is a good bet, because the expected value of the gamble is $1.25 versus the sure outcome of $1.00. Risk aversion is likely an innate intuition that colors the decision-making process.

When Costa and colleagues posed this problem to participants speaking in their second language, risk aversion disappeared, and they took the bet. Apparently, when these people were using their effortful second language, they no longer relied on intuition but thought rationally instead. So, at least from a logical standpoint, they made a better decision in their non-native language.

Cause and effect. We humans want to have a reason for why things happen, so we often make causal explanations even when no such relationship exists. Superstitious behaviors arise in this way. The baseball player who hitches up his trousers, spits out his chewing tobacco, and makes the sign of the cross, in that order, before stepping up to bat really believes those behaviors will increase his chances of hitting the ball.

In the laboratory, it’s quite easy to get participants to believe they’re controlling the behavior of a device — such as a pattern of flashing lights — when in fact what they’ve learned is a pattern. In other words, they think they’re controlling the device when instead they’re following it.

Ordinarily, people fall prey to all sorts of logical fallacies about causal relationships. However, when they need to deal with such situations while using their second, effortful language, they’re less likely to make these kinds of mistakes in their thinking.

Moral issues. Moral thinking is an area where intuition and emotion dominate our decision-making processes. In one famous moral dilemma, you’re asked to imagine you’re on a footbridge over a trolley line. Five workers are on the track, and a trolley is racing toward them. A very large man is standing on the footbridge just above the track. If you push him off the bridge, his large body will stop the trolley. He'll die, of course, but you'll save the lives of the five workers. Would you do this?

A few people say yes, justifying the act from a utilitarian perspective as the greatest good for the greatest number. However, most say no, responding from an absolute moral perspective: Killing is wrong, even if it saves more lives in the process.

Once again, when people are using their effortful second language, their thinking shifts from an intuitive to a rational (in this case, utilitarian) mode. They're more likely to say they'll push the large man off the bridge to save the five workers.

How Thinking Shifts

In all three cases — judgments of risk, causation, and morality — we see a shift from intuitive to rational thinking when people use their second language. At first, this finding is unexpected, since rational thinking itself is more effortful than intuitive thinking. Generally speaking, when we try to engage in two effortful tasks at the same time, we perform poorly at both.

However, it’s also important to understand what makes thinking rationally or speaking a second language effortful. It’s not so much the demand on cognitive resources, as is the case, for example, when doing mental arithmetic or reciting the alphabet backward. Rather, what makes rational thought or a second language difficult is the constant need to inhibit ingrained patterns of behavior. When we speak a second language, we need to inhibit our native language. And when we think rationally, we need to inhibit our natural intuitions.

Brain imaging research shows that the same areas of the brain — mainly in the prefrontal cortex — are activated both in second-language use and in rational thought. Apparently, once second-language speakers activate their brain’s inhibition center, it inhibits their intuitions and emotions, too. As a result, they make more rational decisions when they’re using their second language.


Costa, A., Vives, M.-L., & Corey, J. D. (2017). On language processing shaping decision making. Current Directions in Psychological Science, 26, 146-151.

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