 But there are strong reasons not to equate probability with any actual relative frequency (see entry  interpretations of probability,  §3.4). Many philosophers, including Karl Popper (1967) and David Lewis (1986), have taken Born probabilities instead to exemplify a distinctive kind of objective property (propensity or chance, respectively) that may be ascribed to actual or possible individual events. Lewis took quantum indeterminism to be the last hold-out of objective chance.