The philosophy of perception concerns how mental processes and symbols depend on the world internal and external to the perceiver. Methods of studying perception range from essentially biological or physiological approaches, through psychological approaches, to the philosophy of mind, empiricist epistemology such as that of David Hume, John Locke, and George Berkeley, or Merleau Ponty's affirmation of perception as the basis of all science and knowledge. Using our senses of sight, hearing, touch, smell, and taste, we discover colors, sounds, textures, and so forth of the world at large. 'External perception' or 'sensory perception,' ('exteroception'), tells us about the world outside our bodies. We can sense where our limbs are, whether we are sitting or standing we can also sense whether we are hungry, or tired, and so forth.

Perception is categorized as internal and external: 'Internal perception' ('interoception') tells us what is going on in our bodies. Psychophysical evidence denotes that without this ability, we would find the world very confusing. Size, shape, brightness, and color constancies help us better to understand and relate to world. Likewise, when saying brightness constancy, we understand the perception of brightness as the same, even though the amount of light reaching the retina changes. Color constancy is the inclination to perceive familiar objects as retaining their color despite changes in sensory information. Shape constancy is the tendency to see an object as the same no matter what angle it is viewed from.

The perception of an object as the same regardless of the distance from which it is viewed is called size constancy. The sensory information may change as illumination and perspective change, but the object is perceived as constant. A white house looks like a white house by day or by night and from any angle. Once we have formed a stable perception of an object, we can recognized it from almost any position, at almost any distance, and under almost any illumination. This is because our perceptions have the quality of constancy, which refers to the tendency to sense and perceive objects as relatively stable and unchanging despite changing sensory stimulation and information. Familiar objects tend to be seen as having a constant shape, even though the retinal images they cast change as they are viewed from different angles. Using sensory information as raw material, the brain creates perceptual experiences that go beyond what is sensed directly. Our perception of the external world begins with the senses, which lead us to generate empirical concepts representing the world around us, within a mental framework relating new concepts to preexisting ones. The word perception comes from the Latin perception-, percepio, meaning 'receiving, collecting, action of taking possession, apprehension with the mind or senses.' That means, we sense the objective world, but our sensations map to percepts, and these percepts are provisional, in the same sense that the scientific methods and scientific hypotheses can be provisional. Many cognitive psychologists hold that, as we move about in the world, we create a model of how the world works. Cognitive sciences make the understanding of perception more detailed: Perception is the process of acquiring, interpreting, selecting, and organizing sensory information. In contemporary psychology, perception is defined as the brain’s interpretation of sensory information so as to give it meaning.

Perception definition philosophy