Source: 14 minutes 40 seconds juncture, Lecture 6-1 (transcription, ... How to Reason and Argue, by Prof Ram Neta PhD in Philosophy

So the way we've been using the quantifier all, if you say:   [1.] all ravens are birds,
all you mean is            [2.] there aren't any ravens that are not birds.
But that's not the same as saying    [3.] there are ravens and all of them are birds.

How do 2 and 3 differ? They look identical to me.
For want of concision, please abbreviate ravens as R and birds are B.

  • 2
    It may be easier to see if you used predicate logic. So, [1] would be: For all x, if Raven(x) then Bird(x). [3] would be: There exists x such Raven(x) and for all y, if Raven(y) then Bird(y). May 4, 2015 at 19:16

1 Answer 1


In case 2, it is possible for there to exist no ravens.

  • 1
    This is the right answer. Compare "there aren't any living passenger pigeons that aren't birds" and "there are living passenger pigeons and all of them are birds." The second sentence was once true, the first sentence still is. May 4, 2015 at 20:45

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