The Commens Dictionary

Quote from ‘On the Natural Classification of Arguments’


The formula of analogy is as follows:-

S’, S”, and S”’ are taken at random from such a class that their characters at random are such as P’, P”, P”’.
t is P’, P”, and P”’.
S’, S”, and S”’ are q;
.·. t is q.

Such an argument is double. It combines the two following:-


S’, S”, S”’ are taken as being P’, P”, P”’.
S’, S”, S”’ are q.
.·. (By induction) P’, P”, P”’ is q.

t is P’, P”, P”’.
.·. (Deductively) t is q.


S’, S”, S”’ are, for instance, P’, P”, P”’.
t is P’, P”, P”’;
.·. (By hypothesis) t has the common characters of S’, S”, S”’.

S’, S”, S”’ are q.
.·. (Deductively) t is q.

Owing to its double character, analogy is very strong with only a moderate number of instances.

W 2:46-47; CP 2.513
‘Analogy’ (pub. 06.01.13-19:35). Quote in M. Bergman & S. Paavola (Eds.), The Commens Dictionary: Peirce's Terms in His Own Words. New Edition. Retrieved from
Jan 06, 2013, 19:35 by Sami Paavola
Last revised: 
Jan 07, 2014, 01:01 by Commens Admin