Nitpick: Cartesian philosophy might be obscure, but I don't think it's a failed theory in the sense that, say, the phlogiston theory of combustion is a failed theory.
Even if it was ultimately discarded by philosophers, it allowed the modern field of epistemology to develop (which wouldn't have really been possible previously), and (arguably) contributed to the development of physics by excluding our mental vocabulary (thoughts, experiences, beliefs, etc.) from the study of the physical world. At the expense of our ability to understand said mental vocabulary perhaps, but an improvement on what had been thought previously.
I'd compare it to how a particular module in a program might be important for some time, since it provides some basic functionality that is required in order to develop the rest of the program, but that after some time is no longer needed and refactored out in favour of something more sophisticated.
Of course, and my apologies because I was unclear with my language. I was using Cartesianism as an example of faded, not failed, philosophical field. That was rather foolish of me to word it so lazily. Thanks for the nitpick and pointing out all the great things that resulted.
Even if it was ultimately discarded by philosophers, it allowed the modern field of epistemology to develop (which wouldn't have really been possible previously), and (arguably) contributed to the development of physics by excluding our mental vocabulary (thoughts, experiences, beliefs, etc.) from the study of the physical world. At the expense of our ability to understand said mental vocabulary perhaps, but an improvement on what had been thought previously.
I'd compare it to how a particular module in a program might be important for some time, since it provides some basic functionality that is required in order to develop the rest of the program, but that after some time is no longer needed and refactored out in favour of something more sophisticated.