Recently I’ve been reading a bit of ancient Hindu and early Buddhist thought.  One of the logical devices they used is the “tetralemma,” which has 4 problematic alternatives, just as a dilemma has 2.  For instance, one might ask the question whether the soul lives on after death, and the perplexing answers could be as follows: i) is the soul immortal? –No; ii) is the soul mortal? –No; iii) is the soul both immortal and mortal? –No; and iv) is the soul neither immortal nor mortal? –No.[1]


What is the value of such a ploy, other than to test our patience?


Let’s raise another sort of question, in the spirit of a recent philosophy blog:

Is agreement a sign of rationality?  –No.

Is disagreement a sign of rationality?  –No.

Are both agreement and disagreement signs of rationality?  –No.

Is neither agreement nor disagreement a sign of rationality?  –No.


This tetralemma could encourage us to realize that disagreement doesn’t fit the case when we ask for a sign of rationality.  What does fit the case is rather the ability to entertain a proposition. Agreement or disagreement with a proposition (or with another person) requires not only entertaining the proposition in question but also an act of the will, affirming or denying it.  But affirming or denying can just as easily result from non-rational impulses, such as the impulse to annoy someone, or not to.  Yet there are times when it is rational either to agree or to disagree with a given proposition, and irrational not to.  In a similar way, we might argue against Kant’s universal agreement criterion of objectivity, at least given that the above replies to our four questions are correct.


Let’s take an easier, Buddhist example of a torch that burns all night:

Does the same flame exist all night?  –No.

Does the same flame then not exist all night?  –No.

Does the same flame both exist and not exist all night?  –No.

Does the same flame neither exist nor not exist all night?  –No.


This tetralemma is intended to teach us that a flame is not the sort of thing that can be properly referred to as “the same.”  One flame rather leads to the next in a causal series of momentary flames, serially exhausting their infinitesimally different fuels.  This is the real truth of the matter; if we nevertheless say, “the flame burned all night,” what we are expressing is rather a conventional truth.

In Buddhism, the image of the flame is used to teach us something about the self or the soul.  But that is another story for another day.

[1] See for instance the Majjhima Nikaya, ed. V Trenckner (London: Pali Text Society,1948-1960), I 483-88, as quoted in Mark Siderits, Buddhism as Philosophy: An Introduction (Indianapolis: Hackett, 2007), p.71.