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You have basically already answered your own question. A simple R & C circuit configured as a low pass or a high pass filter circuit is not capable of sustaining oscillation. For oscillation you need something that provides feedback from output to input of the circuit with 180 degree phase shift. Almost always that requires the circuit to contain some type of active component that adds gain so that the oscillation can be sustained. Without it any oscillation from a Time 0 application of the feedback will die out in a few cycles due to the lossy nature of the circuit.