We are typically quite sloppy about distinguishing between physical and mental sensations (memories, mental images, and mental impressions of other physical or mental sensations). These two kinds of sensations alternate, one arising and passing and then the other arising and passing, in a quick but perceptible fashion. Being clear about exactly when the physical sensations are present will begin to clarify their slippery counterparts—flickering mental impressions—that help co-create the illusion of continuity, stability, or solidity.
