“All Ravens are Black” — a meta-investigation

Technique 1

Observe a sufficiently large number of ravens, and determine whether any are non-black.

Examples 1

Raven 1 – black
Raven 2 – black
Raven 3 – black
. . .
Raven N – black

Technique 2

Observe a sufficiently large number of non-black entities, and determine whether any are ravens.

Examples 2

White Snowball 1 – not a raven
Red Pepper 1 – not a raven
Brown Bag 1 – not a raven
White Snowball 2 – not a raven
. . .
Yellow Yield Sign N – not a raven


It may be necessary to make significantly more observations in technique 2 for the same degree of confidence.

On the other hand, it will be significantly easier to find appropriate entities for observation in technique 2.

When stating the results of technique 2, it is good practice (although not strictly required) to observe a single raven*.  If this is not done, the statement of results should include, for clarity of communication, the statement that the observations made do not establish that any ravens in fact exist.

* Note that it is not necessary to observe the color of the raven in this case.

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5 Comments to ““All Ravens are Black” — a meta-investigation”

  1. *laughing and laughing* LOVE this!!! :)

  2. What if one investigates the definition of a raven and finds that black is part of the definition?

    • An interesting point! How to investigate a definition? Maybe do a survey, and say “I hear that in the Ukraine there are white ravens!”, and see how many people say “Really? Let’s look them up in the Wiki-pedia!” vs. how many say “Don’t be ridiculous, if they are white they can’t be ravens!”…

      • Should not time be a consideration? What if once there were multi-colored ravens, but they all perished or changed color? How do we know the ravens will remain black through the course of the investigation, or beyond? Yesterday half a hundred blackbirds (the kind with red wings) carpeted the ground beneath my backyard bird feeder, and then something disturbed them, and as one, with a thunderous whoosh, they took flight.


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