Sensa arise from a confusion between a perception (which is part of the percipient and therefore mental or spiritual) and the object of that perception (the perceptum)

The existence of matter can also not be inferred on the basis of the prima facie existence of what I perceive “by means of the sense organs of our bodies”, i.e., of what he calls “sensa” (NE §373), because it is erroneous to believe that matter as the presumed outside cause of a sensum has the same qualities as a sensum and thus has to exist (NE §365). He conjectures that if there are outside causes of sensa they must be substances which are “of a spiritual nature” (NE §371). When it comes to (c