As J.Z. Smith has noted, comparison is effectively universal as a method for the study of religion (see his “In Comparison a Magic Dwells,” and related essays in Kimberly C. Patton and Benjamin C. Ray, eds. In Comparison a Magic Still Dwells. Berkeley and Los Angeles: University of California Press, 2000). Comparison itself is perhaps the most basic aspect of our perceptual cognition–taking note of contrasts, which accumulate to the perception we have of the world in which we live. Comparison as a method of study is fundamentally, then, noting similarities and differences. However, the comparison of religions and philosophies is often undertaken with a naive presumption that similarities point to a common source that transcends each of the two terms and accounts for their similarity. For example, if a Spanish mystic has written something that sounds like something that a Tibetan lama has written, it means that they are talking about the same thing and that that same thing—because they both talk about it—must exist. (Quite frequently these kinds of claims are made without any acknowledgement of the problems of translation.)
To put it more succinctly: The very act of comparing hypostatizes the two terms of the comparison as comparable.
When such thinking moves from being naive to being theorized, it becomes Perrennialism—the meta-religious system so convincingly, and misleadingly, summarized in the phrase: One mountain, many paths. Neo-Platonic notions of the “great chain of being” provide the cultural basis for this idea, used widely by putatively liberal thinkers ever since the World’s Parliament of Religions (the first one, 1893). I say “putatively” because despite being seen as a way of saying all religions are of equal value, it actually provides those who claim to know the top of the mountain with two further claims of superiority. First, that their own religious commitment is superior because it encompasses all the others. Second, a claim of superiority over those who point out differences between religions as important because those people are caught down on the lower reaches of the mountain, where they can’t see the grand unity. Many contemporary Buddhist Modernists (a.k.a. x-Buddhists) seem to embrace this idea, quoting whatever mystic or spiritual teacher they have cobbled together their own view out of, and replacing the neo-Platonic “One” at the top of the chain of being with the “Dharma.”
Making comparisons between religions is based on the existence of similarities (and differences). Some in the field of comparative religion treat similarity as unproblematically perceptual in nature. Such thinking about comparison as a method is being misled by a bad metaphor: “one sees similarities.” However, similarity is not something that is perceived, but constructed. Using the terms “icon” and “iconicity,” Terence Deacon points out that similarity is an ex post facto conclusion, not a perception. “Icons and iconicity are not merely perception and learning, the refer to the inferential or predictive powers that are implicit in these neural processes.” (Terence Deacon. The Symbolic Species: The co-evolution of language and the brain. New York and London: W.W. Norton, 1997. P. 78. Emphases in original.) To note a similarity is to engage in an interpretive process by which two (or more) things are identified as being similar. One does not see similarity, but concludes on the basis of perceptions that two things are similar. To treat it as if it were a perception is to conceal a host of epistemological issues under an inappropriate metaphor (similarity is a perception).
So, what to do? what to do?
Glenn Wallis has recently noted the importance of new concepts: http://speculativenonbuddhism.com/2013/10/01/a-non-buddhist-encounter-with-the-void/. In thinking about the problems of the comparative method and the need to avoid the simplistics of Perrennialism, I would suggest my friend Peter Yuichi Clark’s phrase “complementary incommensurabilities.” (in his dissertation: “Japanese Americans and Aging: Toward an interreligious spirituality,” Emory, 2001) This phrase captures well the problems of the comparative presumption that the two terms of the comparison are comparable. It also avoids such nonsense as “Is Marxism really a religion?” Of course, once complementary incommensurabilities becomes a slogan, we’ll have to find something else.
Further take home: the project of comparative religions per se is fundamentally flawed (in more ways than this one post can address), and it is best abandoned.