While taking a group of benefactors on a tour through the new aviary they had just helped to build, a noted ornithologist commented, "And here we have two of the finest examples of ravens that I have ever seen. Notice the lustrous black plumage for which all ravens are famous." The ornithologist continued his lecture, commenting on the corvine feeding and nesting habits as well as on the birds' legendary role as harbingers of ill fortune.
When the ornithologist had finished, a young man said, "Sir, excuse me, but did you say that 'All ravens are black'?"
"I don't know if I said exactly that, but it's true. All ravens are black."
"But, how do you know that - for certain, I mean?" asked the young man.
"Well, I've seen a few hundred ravens in my day and every one of them has been black."
"Yes, but a few hundred are not all. How many ravens are there, anyway?"
"I would guess several million. As for your question, many other scientists, and non-scientists for that matter, have observed ravens over thousands of years and so far the birds have all been black. At least, I don't know of a single instance in which someone has produced a non-black raven."
"That's true, but it's still not all - just most."
"True, but there is other evidence. For example, take all these lovely multicolored birds we have seen today - the parrots, toucans, the peacocks -"
"They're lovely, but what do they have to do with your claim that all ravens are black?"
"Don't you see?" asked the ornithologist.
"No, I don't see. Please explain."
"Well, you accept the idea that every new instance of another black raven that is observed adds to the support of the generalization that all ravens are black?"
"Yes, of course."
"Well then, the statement 'All ravens are black' is logically equivalent to the statement 'All non-black things are non-ravens.' This being so and because whatever confirms a statement also confirms any logically equivalent statement, it's clear that any non-black non-raven supports the generalization 'All ravens are black.' Hence, all these colorful, non-black non-ravens also support the generalization."
"That's ridiculous," chided the young man. "In that case you might as well say that your blue jacket and gray pants also confirm the statement 'All ravens are black.' After all, they're also non-black non-ravens."
"That's correct," said the ornithologist. "Now you're beginning to think like a true scientist."
Who is reasoning correctly, the ornithologist or the young man?