两件事情可以单独或联合发生时，两件事情联合发生的概率不可能高于任何一件事情单独发生的概率。然而人们在决策的过程中，会本能地认为一个详细、具体的事情更可能发生。尽管实际上每个细节的添加，都使这件事情越来越不可能发生。

由于合取谬误（conjunction fallacy）这种心理倾向，我们很容易落入假消息的陷阱。虚假故事都是经过精心编造，并且富有丰富细节。由于充满了细节，我们很容易相信这样的假消息是真实的。

这种事情在我们周围随处可见，比如当某人向你讲述一件事时，他讲的细节越多，你越容易相信他讲的是真的。因此有一句话说：细节决定真实。当你知道了合取谬误，下次当你听到充满细节的故事时，你就知道应该提高警惕，问自己一个问题：这是真的吗？

Tversky 和 Kahneman (1983)指出在概率判断中， 如果将两个合取项组成的合取事件的概率估计大于合取项的概率估计， 那么就会产生合取谬误(conjunction fallacy)。用数学表达就是：P (A∧B)≥P (A) or P (B)， 因为根据集合关系， 元素 A∧B∧集合{A， B}， 所以 P (A∧B)≤P (A)or P (B)， 显然合取谬误违反了这一规则。而合取谬误还包括一种特殊的情况：双重合取谬误， 即 P (A∧B)≥P (A)and P (B)。

研究者对这一现象进行了大量深入的探讨，目前解释合取谬误的理论主要包括因果模型理论、惊奇理论、确认理论、加权平均模型理论以及“齐当别”理论等

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.