Usually, my first example is an easy and common one. "Imagine that someone was describing you. They listed all of your best qualities, and the best things you've ever done. Does that give an accurate picture of you? Then, a second person describes you, listing all of your worst qualities, and the worst things you've ever done. Does that give an accurate picture of you? Yet, both are true."
If someone who had never met you listened to both of those descriptions, they'd be confused. They'd probably start trying to figure out which person was lying. The thing is, neither of them are lying! Yet, neither is giving an accurate account of what you are like.
Take any single aspect of a personality - quirks, fears, awards, occupation, anything - and describe the person using only those facts, and the picture is incomplete.
I reminded one of my daughters of this when she was in college. She'd described her sister's idiosyncrasies to her friends in advance of her sister's visit, and then informed us, "They're terrified to meet her. One told me that she wouldn't even know what to say to her."
"That's because the only things they know about her are what you've told them."
"It's all true!"
"Yes, it's true, but it's also very carefully chosen to paint a certain picture."
"No, it isn't! It's all true!"
"True does not necessarily mean accurate."
"Yes, it does! True means accurate!"
It doesn't help that this child tends to define herself almost entirely as "not my sister," so anything different between the two is seen as extraordinarily significant.
(And yes, after they met her, the friends thought that some things her sister did were odd - for instance, her university did not allow people of the opposite sex into the bedrooms of students, so she wouldn't go into any men's bedrooms - but the comment that made it back to us was, "She's a lot more normal than her sister made her sound.")
There's an example that I love to use, especially in class - Surgeon's Photograph.
For decades, it was the most famous photograph purporting to show the Loch Ness Monster. It was supposedly taken by a London gynecologist (a man assumed to be intelligent and sober), and showed the classic long necked "monster" appearance.
Monster enthusiasts were delighted. This was scientific proof, they said, of the creature in Loch Ness.
Doubters pointed out that, in and of itself, a photo proves nothing. Plus, this one had no identifying features to show that it was taken in Loch Ness, and no other objects for scale, to give an idea of the size of the object.
Allow me to digress for a moment to explain "photographic negative" to those too young to remember film. In the days of film cameras, a camera was loaded with a cartridge of light sensitive material, "film." Every time you took a photo, the film would wind from one side of your camera to the other, making one image every time you pushed the shutter button. Rolls of film came in different lengths, so that you could take 12, 24 or 36 photos per roll of film. Then the film was exposed to chemicals that set the image, and the image was in reverse - negative - of the way the print made from it would be; light was dark, dark was light. When film started being able to show color, red was green, etc. on the negative.
To make prints, you needed the negative. If it was lost or damaged, the only way to reproduce a photo was to take a photo of the photo, so you'd have a new negative.
The only way to "retouch" a photo was to painstakingly paint either the photo or the negative. Altering a negative was very difficult.
NASA determined that in the above photo:
1. The negative had not been altered in any way.
2. The printed photo had not been altered in any way.
3. The object and the water were physically present, not a reflection or painting.
4. The object was in motion, going forward.
5. There was a much larger mass, or body, under the water.
6. The forward motion came from the movement of some part of the mass or body under the water.
Monster enthusiasts were delighted, again. This was scientific proof, they said, of the creature in Loch Ness.
Decades after the NASA analysis, a man came forward to say that he, not the surgeon, was the photographer, and that the photo was a hoax. He'd sculpted the head and neck, he said, and attached them to a toy submarine. He then put the toy sub in the shallows of the lake, and took the photo.
For me, here's where the story becomes fun. Not one single determination of the NASA analysis is inconsistent with the toy submarine story. All of those conclusions can stand as absolute truth, and the toy sub hoax can be accepted as true.
In fact, most researchers and others now consider this photo to be a hoax - but a very successful hoax.
There are a handful of folks who say that the hoax story is the fake one. For instance, the supposed hoaxer said that the original intent was to embarrass the Daily Mail, the newspaper that first printed the photo. If that's true, they ask, why did he wait decades, until most of the Mail employees from the 1930s were dead, to reveal it? They also point to other bits of analysis, including a note in the NASA analysis that says it is possible that there are whiskers on the animal's face.
All of those things could, in fact, be true, without discounting any of the NASA analysis.
See how much fun that can be? Each side can claim that the hard evidence is on their side, and they can do so without lying, or even trying to be deceptive.
Once when I was teaching my debate students about when and how to challenge evidence, I said that it's possible to ask for the credentials of any quoted experts. "Dr. John Doe says, in an article published in X journal..." might be entirely true. But, if the subject is medical research, and Dr. Doe's doctorate is in Medieval English literature, well, he wouldn't be a particularly credible source.
"Only use this information to discredit your opponents," I said. "Don't go putting things that sound good but are total bunk into your own arguments."
"Oh, sure," said one student. "Like you're going to teach us this stuff, and we're not going to use it for The Dark Side."
(And therein lies the problem with knowledge. And adolescence.)
"Just remember," I tell the students, "just because something is true doesn't mean that you're getting the whole story, or an accurate picture."
I remind them of one of my favorite Mark Twain quotes: "There are three kinds of lies: lies, damned lies, and statistics."
