I met an installation artist at a dinner party a couple of months ago. When she asked what I did, I told her I was a physicist.

"I love physicists," she gushed. "I work with a tribe in the Amazon and they are more quantum mechanical than us."

"What do you mean?" I asked.

"Quantum mechanical, you know...more spiritual, less materialistic than the Western world. "

Physicist Wolfgang Pauli's phrase came to mind: "That's not even wrong." I had the decency not to say it, but instead pointed out that she was using the words "quantum mechanical" inappropriately.

"They're not your words," she said. "I can use them as I please."

Of course. In her eyes, science is rife with outrageous ideas, so why wouldn't her outrageous analogy be equally valid?

Once I overcame my frustration, I started to think about the misuse and misunderstanding of scientific ideas. What distinguishes an outrageous idea from a reasonable one? And how are these different from a true or a false idea? I suspect that many people confuse reasonable/outrageous with true/false, which contributes to difficulties they have in understanding the sometimes counterintuitive scientific findings.

To address this confusion, I offer pragmatic definitions (quibblers, you have been warned!) of the words reasonable, outrageous, true and false as they apply to scientific ideas.

An idea that I find reasonable is one that fits with my perceptions and current knowledge. An outrageous idea doesn't agree with my perceptions or preconceived notions of reality i.e., current theories of the natural world. (The word current is key: an outrageous idea can become reasonable over time.) A true idea has been thoroughly tested and agrees with available evidence. Note that scientific truths are provisional and can be upended by new evidence. A false idea is one where theory and reality don't agree. That is, the phenomenon being studied can be explained by a different concept than the one proposed or it cannot yet be explained.

By combining the reasonable/outrageous categories with the true/false one, we can gain insight into how science works (see table below).