What reasoning flaw is used in assuming that every member of a defined group shares the same characteristics based on a few instances?

The reasoning flaw that arises when assuming that every member of a defined group shares the same characteristics based on a few instances is known as "Selected Instances." This flaw occurs when broad generalizations are made based on a limited number of examples, leading to conclusions that may not accurately reflect the actual attributes or behavior of the entire group. Such reasoning overlooks the diversity and variability among the members of the group and assumes homogeneity where it may not exist.

For instance, if someone observes only a few individuals from a particular demographic who exhibit a certain trait and then concludes that all members of that demographic possess that trait, they are committing the Selected Instances flaw. This can severely misrepresent the reality of the group’s composition and can lead to stereotypes.

Understanding this concept is crucial in both interpreting arguments and constructing valid ones, as it emphasizes the importance of comprehensive evidence when making claims about populations based on specific examples.