Perusing the media coverage of science news, I am often struck by words such as ‘fact’ and ‘scientific theory’ being used roughly interchangeably. While not the most sexy of aspects of science, the meaning behind these words represent some very specific ideas that help us construct our understanding of science and more importantly, our critical appraisal of the meaning and significance of any reported story. So here is a quick round-up of the ideas behind such words.

To start off, words like hypothesis and theory have very specific meanings in science, and not necessarily the same as in common speech. Let’s start off with a fact. A fact is simply an observation, like ‘the sun rises and sets every day’, descriptions of what is there. Crucially, they do not explain why something is, nor predict what is going to happen in the future. From the observation, we can make a hypothesis to explain the fact. The sun might be affixed to a celestial dome that constantly moves or alternatively, the sun and the earth might be two spheres and the rotation of the latter causes the sun to appear and dissapear on a 24-hour cycle.

In order to decide which hypothesis is likely to be true, we go and make some more observations (e.g. sending a satellite to orbit to take some pictures) to generate evidence. Therefore, we can call the hypothesis that is supported by evidence a theory. A theory has three important facets; a) it provides an explanation for the fact, not just a description, b) it predicts future behaviour – e.g. if the Earth keeps revolving, the sun will rise and set tomorrow and c) it is falsifiable; if we find new evidence against our current theory, we can discard it as false.

These five concepts (fact, hypothesis, evidence, theory and falsifiability) are at the core of the scientific method and the way we do and interpret science. With these, we can now go and read articles with a critical eye and a critical mind.

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Disclaimer: The explanation above is an unashamedly post-positivist, Popperian approach to the scientific method. Nearly all of it would be considered debatable to an epistemologist, but it is aimed to represent the current majority consensus amongst practising scientists.