What's a Theory?

This question was prompted by the fact that so many people get it wrong.

This one gets my goat, and if I sound at all grumpy while typing this, then GOOD.

"It's just a theory."

I see it in the news, and on twitter, and plastered all over the internet... 'It's just a theory'. That phrase repeated over and over again like a mantra from the phrasebook of people who don't want to accept that something's true but don't quite understand how to argue against it properly.

The problem is this: The problem is with certain people's understanding of that word. The kind of person who will attack evolution, for example, by saying 'it's just a theory' is the kind of person who thinks that a 'theory' is simply an idea that someone had. Something that sprang into their head on Sunday morning while they were trying to decide which jam to have on their toast. As if coming up with a theory is as simple as saying "I think this happens because that does," and then getting on with your day.

Well they're wrong. What's being described there is not a theory. It's an idea. A supposition, if you will. At the extreme ends of what's actually being described, we might even get away with labelling it a hypothesis, but it's not a theory.

It's a Theory

A theory (and I've typed that words so many times that it's starting to look like it's not spelt correctly any more) is this:
A proposed explanation for measurable phenomena that makes predictions that can be tested empirically and therefore be supported or contradicted by observation.
An accepted theory, such as those that go towards defining our current best understanding of evolution, is one which has made predictions which have been tested and are supported by empirical observation- that is real-world testing and measurement.

An idea which cannot be used to make predictions, or makes predictions which cannot be tested, is not a theory. An idea which has made predictions which have been tested and found to be false is a theory that is wrong.

The Bottom Line

The use of "it's just a theory" as an argument against something, whether that's in conversation, a news report or a tweet, does nothing, absolutely nothing but provide the recipient with evidence of the ignorance of the person using it.

So don't use it!


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