Science & Society

Critical Thinking: Sooner or Later, Your Assumptions Will Kill You

Written by Bruce R. Copeland on September 04, 2008

Tags: assumption, critical thinking, extrapolation, hypothesis, law of nature, science, scientific reasoning, theory, uncertainty principle

This is literally true.

An assumption is something we think is true, but which we have not thoroughly tested or proven. Often it is based on an extrapolation or a parallel. Careful handling of assumptions is essential to critical thinking.

Everyone makes assumptions. It’s pretty much the only way to get anything done, given that it is impossible to have complete knowledge about everything (a law of nature called the Uncertainty Principle).

Scientists are no exception. In science there is a structure for using assumptions.

Assumptions differ from theories and hypotheses. A hypothesis is a very specific line of reasoning designed to be tested using the scientific method. A theory is general, and if true, should apply in all specified circumstances. Assumptions are based on observation of specific instances and may be true only for that particular set of cirmcumstances. Assumptions are supposed to be explicitly spelled out in any kind of scientific reasoning.

Assumptions are the root of many conflicts and misunderstandings in and between science and society. For example, scientists and doctors often assume that all humans have the same physiology because of our overwhelming genetic similarity. This is a bad assumption for a number of reasons. Our genes, though similar, are not all identical. Furthermore their expression in our physiology depends on development, which is influenced by environment. As a second example, non-scientists sometimes assume that if large amounts of nuclear radiation or certain chemicals are deadly, small amounts must also be dangerous! Further examples of common bad assumptions: If scientists haven’t yet thoroughly proven something, then it must not be true. If something was never a problem in the past, then it won’t become one tomorrow. If two things are correlated, then there must be a cause and effect relationship between them… You get the idea. A big part of the problem is that neither scientists nor non-scientists are careful about spelling out their assumptions in public discourse. Another part of the problem is that none of us reevaluates our assumptions often enough.

Whether in science or everyday life, we could all stand to be more careful with our assumptions. We need to recognize them when we make them, test and reevaluate them periodically, and clearly point them out in communication.

Throughout life we make a lot of assumptions, and some of them aren’t too good. For each of us, one of those bad assumptions will eventually be our undoing. The question is, which assumption will it be?