The exception proves the rule

You may have noticed from a previous post, Sniffing out litter, that I'm not too proud to pick up other people's litter. One of the more obvious observations is that litter breeds litter. Once a space has been completely cleared there's a noticeable delay before litter starts accumulating again. Trying to see if my observations were backed up by hard evidence I came upon a paper published in 1990 entitled "A Focus Theory of Normative Conduct: Recycling the Concept of Norms to Reduce Littering in Public Places" which describes a series of experiments carried out on subjects who'd been visiting a University Hospital and were returning to their parked cars.

On leaving the building the subjects were given a handbill, a potential piece of litter, and their subsequent behaviour was observed. The key variable was how much litter there was in the space between the entrance and the car park. To draw attention to the existing state of the space a confederate experimenter deliberately dropped a large piece of litter in front of the subject. A second confederate then decided if the subject had witnessed this and then noted if the subject then dropped litter themself.

The key finding of this part of the experiment was that if they'd seen someone drop litter into a clean space then this made it less likely that they'd drop litter themself and if they saw someone drop litter into a well littered space then it made it more likely they'd do it themself. The explanation being that witnessing the litter being dropped drew attention to the state of the space and thereby established the prevailing social norm. 

A second experiment simply looked at the space, counted the existing number of pieces of litter, and timed how long it took for the next piece to be dropped. Surprisingly the longest time wasn't for when there wasn't any litter at all but for when there was exactly one piece. The explanation being that a single piece draws more attention to the prevailing social norm than if there's no litter at all. Clearly, the best strategy remains to pick up everything because then the time for the first piece of litter to be dropped gets added to the time from the first to the second.

As a rather literal minded youngster, I was always confused by the saying "the exception proves the rule". To my mind if there was an exception this meant that there wasn't a rule. I later came to realise that all it meant was that identifying something as an exception suggested that there must be a rule for it to be an exception to. 

A few bits of litter are just enough to draw attention to the fact that only a minority of people are dropping it and that therefore the social norm, in this particular place, must be not to.