In their famous 1976 paper, Marr and Poggio start out by saying:
Complex systems, like a nervous system or a developing embryo, must be analyzed and understood at several different levels. Of course, there are logical and causal relationships among them, but the important point is that these levels of description are only loosely related. The underlying philosophical issue here is that reductionism does not imply constructionism.
(the levels they mean here are Marr's levels of description of a neural system, computational, algorithmic, etc.)
What does the last sentence mean? I know what reductionism is, of course, but have never heard of constructionism. A brief search seems to point at something used in the context of education, a concept similar to experiential learning. Is this related?
Please note that I'm not an expert in philosophy, so I would appreciate a non-technical answer.