Common sense

Common sense is judgment that is not based on knowledge or evidence but merely seems to be true or make sense. It is a very useful tool for reasoning, but it is fallible.

Common sense does not make use of the Scientific method, which is more likely to answer questions correctly. Many "common sense" phrases such as "opposites attract," and "birds of a feather flock together" are not only contradictory but often do not stand up to scrutiny and critical thinking.

Example
Consider the following situation:

A school issues a new policy banning the use of headphones for listening to music during study hall. The school administrators used their common sense to judge that students would be more productive if they were not distracted by their music, and that they should ban headphones. The students' common sense, however, can lead them to the opposite conclusion. They may feel that the music helps them to block out distractions and focus more effectively on their work.

"Common sense" that has been disproved

 * Opposites attract: studies have shown that similar couples are more likely to be successful and that similarity is the key to marital longevity.
 * Spare the rod, spoil the child: psychologists refer to this idea as "authoritarian parenting" and it is not only less effective than other parenting methods, but if taken too seriously it can lead to serious mental and physical harm.