Ideas, Locke observes, can become linked in the mind in such a way that having one idea immediately leads one to form another idea, even though the two ideas are not necessarily connected with each other. Instead, they are linked through their having been experienced together on numerous occasions in the past. The psychological tendency to associate ideas through experience, Locke says, has important
implications for the
education of children. In order to learn to adopt good habits and to avoid bad ones, children must be made to associate rewards with good behaviour and punishments with bad behaviour. Investigations into the
associations that people make between ideas can reveal much about how human beings think. Through his influence on researchers such as the English physician
David Hartley (1705–57), Locke contributed significantly to the development of the theory of associationism, or associationist psychology, in the 18th century. Association has remained a central topic of inquiry in
psychology ever since.