An individual's preconceptions are his or her concepts of what things are, e.g. what someone's idea of a horse is, and these concepts are formed in a person's mind through sensory input over time. When the word that relates to the preconception is used, these preconceptions are summoned up by the mind into the person's thoughts. It is through our preconceptions that we are able to make judgments about the things that we perceive. Preconceptions were also used by Epicureans to avoid the paradox proposed by Plato in the "Meno" regarding learning. Plato argues that learning requires us to already have knowledge of what we are learning, or else we would be unable to recognize when we had successfully learned the information. Preconceptions, Epicureans argue, provide individuals with that pre-knowledge required for learning.