Fallacy of Common Sense

We are all familiar with the term “common sense”, or are we?


Common Sense” can be defined as a shared set of understandings that should lead to “good” decisions or judgments.


The concept of “common sense” breaks down when we examine what information humans possess as shared, including models of good decision making and logical outcomes. This has always been an interesting topic for me as a human factors expert. Designers often point to “common sense” as an effective design strategy and rationale to exclude data driven evaluations for Human-Centered Design concepts. Although common, it’s faulty logic.


The fallacy occurs because we assume that our personal experiences, learned behaviors, and decision-making models extend to those around us in the same manner. We often believe that our understanding translates to a logical set of expectations and outcomes: “I am human, and thus I must understand the cognitive models of all humans and their associated decision-making strategies”.


How is this faulty?

Simply put: no two individuals have a life that is a carbon copy of another or perceive and interpret events in the exact same way. Every human is individually shaped by everyday experiences, genetics, environmental influences, educational experiences, social interactions, cognitive models, sensory input, etc. That is not to say humans do not have shared ideologies and experiences, we certainly do, but the level of shared is not as universal and explicit as we have traditionally understood. The disconnect in understanding can be attributed to all of the variables acting upon us every day; the more diverse our experiences in life, the less we share as common between individuals and populations.


When we recognize an act or behavior that violates our individual definition of “common sense” we tend to believe that this individual or group lacks it. In reality, we are observing that “common sense” could be better understood as “commonly uncommon”. Meaning, “common sense” is only common to you!

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