A conjunction fallacy is a type of probability fallacy in which people, when offered the choice between one event and that event plus another event, are more likely to choose the second option as more probable. In other words, some people presented with the question “What is more likely to occur: a dog running across a street, or a dog running across a street and barking at a cat” tend to choose the second option. A conjunction fallacy occurs because people often do not consider that for a conjunction to be true, each part of it must be true, and because options with greater quantity are somehow more attractive.
The basic concept behind the conjunction fallacy is the way in which people tend to view two similar options. In this instance, the options are two types of events or situations in which one is part of the other. An example of how this fallacy can occur would be the following statement: “A man wakes up every day at six in the morning. When he wakes up, is he more likely to drink coffee, or to drink coffee and then brush his teeth?” In answer to this question, people often have the tendency to choose the more complex answer and commit a conjunction fallacy.
The key to recognizing the conjunction fallacy is in understanding and knowing how to identify it. Statistically speaking, a conjunction must be considered as two separate parts, such as “the man drinking coffee” and “the man brushing his teeth.” This means that the second option has two elements that must both be true for it to be more probable than the other option, which only has one element that must be true. Since the second option in a conjunction fallacy contains the first, it is easier for the first option to be true, as it does not rely on a second possible element.
This means that the simpler option is more probable, by the very nature of the argument. Even people aware of the statistical reality behind the conjunction fallacy can easily fall into it, due to the fact that it seems to be innately more appealing. For some reason, people seem to prefer an option that is more complex or seems more developed and decide that it is a more likely or probable situation. This is why someone must understand and know how to recognize the conjunction fallacy to avoid it, as mathematical or statistical background may not be sufficient.