Grouping of things into larger groups is categorization. Mental representation of a category is a concept. Medin (1989) argues concepts and categories serve as building blocks for human thought and behaviour. Lamberts and shanks (1997) argue how concept are mentally represented is a central concern to cognitive psychology. Concept: mental representation of some object, event, or pattern that has stored much of the knowledge typically thought relevant to the thing. Category: class of similar things that share one of two things: Or some similarity in perceptual, biological, or functional properties. Medin says categories are existing objectively in the world and concepts are mental representations of categories. Medin & smith (1984) argue concepts help us establish order in knowledge base. Concepts allow us categorize, to treat new things in same way we treat familiar things that we perceive to be in the same set (neisser, 1987) Categorization allows us to make predictions and act accordingly.