Common-sense metaphysics

Infant metaphysics
Infants make strong ontological inferences about how the world works and what kinds of things it contains. Developmental psychology studies the stages in which the metaphysical lessons are learned.

Infants make the following metaphysical inferences: Some of these conclusions are not reached when an infant has autism.
 * that the world contains rigid objects that are continuous in space and time
 * they treat any surface that is cohesive, bounded, and moves as a unit as a single object. When one solid object appears to pass through another, these infants are surprised.
 * Babies less than a year old distinguish causal events from non-causal ones that have similar spatio-temporal properties
 * they distinguish objects that move only when acted upon from ones that are capable of self-generated motion (the inanimate/animate distinction)
 * they assume that the self-propelled movement of animate objects is caused by invisible internal states -- goals and intentions -- whose presence must be inferred, since internal states cannot be seen
 * When an adult utters a word-like sound while pointing to a novel object, toddlers assume the word refers to the whole object, rather than one of its parts

With newborns, as far as anyone can tell, raw sensory data stimulate them but do not take on meaning; they cannot differentiate between themselves and anything beyond themselves. Self-awareness is widely believed among psychologists not to develop until mid-childhood, and arguably is present in only a few species of animals. Tests performed for self-consciousness include applying a dot on a subject's body, and then placing them in front of a mirror – if they start to investigate the dot, it appears that they may realize their own existence in a self-aware sense. Other species will assume that the animal in the mirror is another animal.

Object permanence is an important stage of cognitive development for infants. Numerous tests regarding it have been done, usually involving a toy, and a crude barrier which is placed in front of the toy, and then removed, repeatedly (peekaboo). In early sensorimotor stages, the infant is completely unable to comprehend object permanence. Psychologist Jean Piaget conducted experiments with infants which led him to conclude that this awareness was typically achieved at eight to nine months of age. Infants before this age are too young to understand object permanence, which explains why infants at this age do not cry when their mothers are gone. "Out of sight, out of mind." A lack of Object Permanence can lead to A-not-B errors, where children reach for a thing at a place where it should not be.

Studies in recent psychology also suggest that three dimensionality is not intuitive, and must be learned in infancy using an unconscious inference. (see depth perception)