We think a single immoral act will start someone down a "slippery slope"

Just as people talk about "gateway drugs" supposedly opening the door to the use of harder substances, so we often say that someone is on the "highway to hell" when it comes to immoral or illegal activity. If someone starts committing petty crimes, for example, it is sometimes assumed that they will move on to more serious criminal activity. Now a new study in Personality and Social Psychology Bulletin suggests that this belief that immoral behaviour will lead the perpetrator down a  'slippery slope' is pretty common.

Past work has already found (fairly unsurprisingly) that we have a negative opinion of people's overall character after we witness them commit an immoral act. But the new study looked at how we believe people will change over time after committing such acts.

In the first study, participants read one of two stories, both about a man returning to his car to find another car parked too close to his own. In the immoral act condition, they read that the man became angry and punched a hole in the tires of the other car with a screwdriver; in the no immoral act condition, the man simply drove away angry. They then answered various questions about the man's character and behaviour both in the past and in the future. These included rating his moral character, rating how likely he would do something unethical or illegal, and indicating whether they thought he would commit five specific acts: damaging someone else's car, breaking someone else's property, stealing, assaulting someone, and drunk driving.

As expected, those in the immoral act condition exhibited a slippery slope effect: they rated the man as being more immoral, and more likely to commit the five specific immoral acts, in the future compared to in the past. The team suggests that this is because single acts of immorality "change the anticipated trajectory" of someone's moral character and behaviour, thus leading us to believe that they will behave more immorally in the future.

In a second study, participants even believed that a person who had merely intended to commit an immoral act was heading down a slippery slope. All participants read a story about a student so nervous about an exam they were considering cheating. In the no attempt condition, the student considers but decides against cheating; in the immoral attempt condition, he tries and fails to cheat; and in the immoral act condition he successfully cheats on the exam. Participants then assessed the moral character and behaviour of the student both in the future and in the past as in the first study.

As in the first study, participants believed that the character who had committed an immoral act was on a downward trajectory – they rated them as having a worse character and more likely to perform immoral acts in the future than in the past. The same was true for the character who merely attempted to commit an immoral act.

A third study found that we think people who have started down a slippery slope will be even worse after a longer period of time. Participants believed a character who had committed an immoral act – in this case stealing –  was more likely to steal again one year rather than one week in the future. Participants also thought that the character would feel less guilt or shame one year in the future compared to one week later, suggesting that we see people's internal moral code as becoming more corrupted with time,  and that this could be why we believe them more likely to engage in immoral acts.

This idea was supported by a final study, which found that the slippery slope effect was counteracted when a character was portrayed as experiencing regret after committing an immoral act. When they didn't seem to experience any internal emotions but were simply punished, there was no impact on the slippery slope effect.

The research suggests we believe immoral behaviour will lead people down a slippery slope. But it doesn't explore whether people actually do go down a slippery slope. Just as the idea of gateway drugs is contentious, so too may be the assumption that our behaviour is bound to get more immoral over time. It would also be interesting to explore whether these beliefs have real life implications: if we think someone is going to become more immoral over time, does that change the way we treat them? Considering that many of us may at one time or another sit on a jury, this may have significant implications.