What color is the sky on an average, cloudless day? Blue is a fair answer, but how do we know that this is true? How do we know anything is true?

Maybe it’s strange to start off with a philosophical question, but it’s a vital first-step that helps bridge the gap between thinking about human psychology and psychological science. At the heart of science is the method used to decide what’s true. For anyone who has an introductory knowledge of epistemology (philosophy of knowledge) or philosophy of science, well you probably know more than I do. But I figured I should start here.

Science, like anything else, has some assumptions. One: the effects we observe in the world have causes (cause and effect exist). Two: observation (and measurement) gives us information about cause and effect. Three: the relationship between cause and effect has a stable pattern. So putting it all together, something is true when it explains and predicts measurable/observable reality consistently. Most accurately, it’s the closest approximation of the truth until a better idea improves or replaces it.

There are alternatives way to view the world, but the most scientific aspect of psychology is its use of the scientific method and the mutual understanding among scientists about what constitutes knowledge. If an idea fails to predict patterns in measurable reality, it just doesn’t pass the test. If a new idea makes better predictions, explains more or fixes inconsistencies, it replaces older ideas.

So how can we apply these concepts to the color of the sky? One of the first tasks is to determine what exactly we’re observing/measuring when we ask the question. There’s the physical aspect of the light, but that’s not what we really asked. We asked for the color: a subjective experience. How do we establish “truths” about something subjective?

There’s a history of debate about what psychology should study. There was a time the behaviorists won most arguments: psychologists should exclusively study what is observable externally (behavior). But modern psychology deals with the ABC’s of the mind: affect (feeling/emotion), behavior and cognition (thought). And it turns out there ARE patterns in subjective experience insofar as we can measure them. Our fully colorblind friends see the same dominant wavelengths of light in the sky (450-485 nm), but they lack subjective perception of color. Even if all we did was ask people to “name the color you personally perceive the sky to be,” we would find at least two groups of people: those who call it blue and those who do not.

This is the type of knowledge we can find about subjective experience: kinds (categories) of people, dimensions of experience (e.g., light intensity from dark to painfully blinding), correspondence between cause (wavelength of light) and effect (color perception). Inconsistencies merely represent research opportunities: is there another group of people we aren’t accounting for? Is there another factor that shapes color perception? Is it the perception that is truly different, or is it the way people communicate their perception? Is there a better way of thinking about color perception? Or perhaps the way we measure it needs to be improved?

So when is something true, and is the sky blue or not? It’s true in psychological science when the data shows a consistent pattern, preferably in multiple sample groups collected in a rigorous way. Interpreting the results, however, is tricky. It’s not like we can say “the sky is definitely blue” or “it definitely is not.” Instead, we have to talk about kinds of people and dimensions of possible perception. The sky is blue-ish for most color-seeing folk, but some see it as light grey. Does this complication mean there was nothing learned? I would say no; we definitely learned something about human minds. It may be complicated, but the answers should be complicated because people are complicated.