The skeptics’ strongest argument is that two years before Kelulé’s 1856 paper, benzene had already been depicted as a hexagon in a book by French chemist A. Laurent, which Kelulé knew and proposed to translate into German.[xiii] Did the depiction undermine Kelulé’s claim to originality? Apparently not. In line drawings, a circle can mean either a disc or a ring; the ambiguity can only be resolved by context. Laurent used the hexagon in the same page to represent benzene, benzoyl chloride, and ammonia, whose structure was a pyramid. Accompanying explanations suggested that his hexagon depicted not a ring structure but was simply the artist’s rendition of a molecule as a chunk capable to bind with other chunks.

A hexagon with “Bz” on it printed in a chemistry book was a suggestive image. Why did it fail to inspire Laurent himself of the benzene ring structure? Why did it fail to inspire Kelulé on the spot? Why did he have to wait for his snake dream? No one can answer this question, but one can venture some guesses. Perhaps his research was not advanced enough. Here I offer a point that is also relevant to serendipitous discoveries. Cognitive psychologists have found that what one sees is at once more and less than what strikes the eyes, being influenced by the meaning one anticipates or attributes to it. Some experiments on vision find that when reading, we see the meanings and not the shapes of the words. Readers of Laurent’s diagram may simply see a chunk and never see the alternative interpretation of a ring. This is not unusual. Serendipitous discoveries often involve a phenomenon that many people have encountered before one person sees it in a new light and recognizes its significance. This happened in the case of antibiotics, as we see later.

Skeptics claimed that Kelulé got the benzene-ring idea from Laurent’s diagram and invented the dream story to avoid giving credit to the French, whom the German loathed in that time of rampant nationalism. Such accounts of “the social construction of science” are now popular. They are not impossible, but not more probable than the dream story. Let us assume for argument’s sake that Kelulé did get a mental jolt from Laurent’s diagram. Does this imply that he stole credit on a sociological motive? Or could he have honestly forgotten the origin of his inspiration? Again cognitive psychology can help. Whatever jolt Kelulé got could not be strong, because he took more than a year to publish the benzene theory. During this time the source of the hexagonal image may have faded from memory. Memory researchers have found that attributing an idea or a piece of information to a wrong source is very common. Many people misremembered how they got the news even for such memorable events as the Kennedy assassination or space shuttle Challenger explosion. With no intention whatsoever to lie, eyewitnesses sometimes mistake what they heard afterwards for what they saw on the crime scene. Misattribution is a weakness for memory per se. However, cognitive psychologists argue that it has evolved because it can also be beneficial to a person as a whole. Human memory capacity is limited. Most although not all sources are quite irrelevant to the contents of information, and forgetting them spares scare mental resources for tasks more important for survival.[xiv] The cognitive psychology of memory provides an alternative explanation to nationalism-motivated lying: Kelulé did not refer to Laurent because he had a lapse in source memory. They also help us to understand the unending credit disputes in the scientific community. In a culture where people freely exchange ideas and tidbits thereof, many half-baked, it is not surprising that a scientist has an idea and, not remembering where it came from, claims it his own.