Complementarity

Actually it is strange that I haven’t written here about it before: the so-called complementarity thesis. It’s strange, for this thesis has influenced my thinking a lot. Even more, it is one of the leading ideas I used in my PhD thesis on the method of understanding. I realized this omission, when I read the last issue of the Dutch Algemeen Nederlands Tijdschrift voor Wijsbegeerte (General Dutch Journal for Philosophy), devoted to the question: “Which philosophical idea deserves wider attention?” The first idea discussed was complementarity, an idea that first has been developed by the Danish physicist Niels Bohr in his debate with Werner Heisenberg. However, since I got it from Karl-Otto Apel, who also has written much about it, I’ll discuss his version.
When Apel discussed the complementarity thesis, there was a hot debate going on on the question whether there is a distinction between the method of explanation, especially used in the natural sciences but also in psychology and the social sciences, for instance, and the method of understanding, used in the humanities and also in psychology and the social sciences. Sometimes explanation is seen as a “hard” method that gives concrete results, while understanding is seen as a “soft” subjective method founded on empathy. Apel wanted to make clear – especially in his Die Erklären-Verstehen Kontroverse in transzendentalpragmatischer Sicht (= The controversy between explanation and understanding from a transcendental-pragmatic perspective) – that a thus conceived distinction between both methods is not correct and that explanation and understanding are just different approaches with different purposes. He did this with the help of Bohr’s complementarity thesis.
What we often see, so Apel, is that the methods of explanation and understanding are associated with different types of sciences (“sciences” understood in the German and Dutch sense, so as all kinds of systematically gathering knowledge, including the humanities and not only the exact sciences). Then explanation is the method of the physical sciences and the science-based approaches of the social sciences and the like, while understanding is the method of the humanities. However Apel’s thesis is (and mine as well) that explanation and understanding are different approaches that can be used in all kinds of sciences (in the broad sense, as just explained). For what is relevant when you gather knowledge is not the field of investigation as such (physical sciences vs humanities) but the type of questions you ask when gathering knowledge. If – my words – you are interested in causes, laws, objective connections etc., you use the method of explanation. In this case you ask why-questions. If you are interested in reasons, motives, or the meaning or sense that something happened, you use the method of understanding. Then the leading questing is the “what … for”-question. Especially (but certainly not only) psychology and sociology are the meeting points of both types of questions. For instance, we want to know why John murdered his father. Then we can ask whether John has an Oedipus-complex, whether he is a psychopath, whether he had used drugs at the moment of the murder, etc. In this explanatory approach we see John as an object drifted by objective forces “external” to him, so to speak. However, we can John also see as a subject with reasons and motives, and then we ask him himself what made him kill his father. Maybe John will tell us that he had been sexually assaulted by his father when he was a child, or, that his father always beat his mother and that he wanted to take revenge. Then we try to understand John and what he did.
As this example shows, explanation and understanding do not need to exclude each other but they are different methods to gather knowledge that can be used alongside each other: both methods are complementary. This made Apel formulate his version of the complementarity thesis:
“Understanding and explanation ... are complementary forms of knowledge corresponding to complementary leading knowledge-interests. That is to say, they
(a) supplement each other within the whole household of human knowledge, so to speak, and at the same time,
(b) they exclude each other as different interests or intentions of asking questions, and,
(c) for both reasons, they cannot be reduced to each other.”
(1979b:12‑13; italics mine).
Now it is so that complementary in this sense is not limited to the methods of explanation and understanding. It is a wider phenomenon. Actually, methodical complementarity is a special instance of the dual aspect view that says that the world as a whole and man in particular can be considered in two ways: objectively and subjectively. For example, man can be considered either as a biological body or as a conscious and thinking subjective mind, as we just have seen. Or, to take another example, nature can be considered as a natural, so physical process, or it can be considered as it is subjectively experienced and constructed (a duality that is important to take into account in this age of global warming and a decreasing biodiversity). But don’t take the complementarity thesis and the dual aspect view in the wrong way. They are ways to look at the world around us. The complementarity thesis and generally the dual aspect view stress that the world or whatever we want to study can be approached from different sides and can be seen from different angles. In the end the world is one. 

Sources
- Apel, Karl-Otto, Die Erklären-Verstehen Kontroverse in transzendental pragmatischer Sicht. Frankfurt am Main: Suhrkamp Verlag, 1979a.
- Apel, Karl-Otto, “Types of social science in the light of human cognitive interests”, in: S.C. Brown (ed.), Philosophical disputes in the social sciences. Brighton, Sussex: Harvester Press, 1979b; pp. 3‑50.
- My PhD thesis (see the column left on this blog page).