Color constancy is stability in perceived color across changes in illumination (and scene composition). Visual size constancy is stability in perceived size across changes in distance. What all perceptual constancies have in common is that the varying property affects the local stimulus features thought to be responsible for the perception of the stable property. It's this (partial) stimulus-independence that makes constancies interesting to both philosophers and empirical cognitive scientists. Other than this minimal common ground there is almost no consensus on what constancies are or how to explain them. Are they the product of unconscious sensory mechanisms or the product of of (potentially) conscious inference? Relatedly, do distant objects look smaller even though we know their physical size or is the size they look to have independent of viewing distance? The best characterization of the stability involved in constancies is also a subject of contention since objects often look both the same and different across the variation in viewing conditions. I will offer a general approach to perceptual constancy that addresses these (and other questions) which has as a consequence that the answers to the questions vary according to details of the property perceived and the circumstances of perception. I will also make some remarks about appeals to introspection as a way to settle these questions.