Observe a sufficiently large number of ravens, and determine whether any are non-black.
Raven 1 – black
Raven 2 – black
Raven 3 – black
. . .
Raven N – black
Observe a sufficiently large number of non-black entities, and determine whether any are ravens.
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.