"persons seem to retain only those words which fill some conceptual 'slot' or need in their own mental structures. A new word encountered for the first time which fills such a conceptual 'slot' is picked up and retained without conscious effort, and it will 'pop' into the mind again when the conceptual need for it arises, even though in the meantime the word may not have been encountered for many months or even years. If there was no conceptual slot that needed to be filled, that is to say, no meaning for which the individual has a use and which the word serves to symbolize, it is exceedingly difficult to make the definition of the word stick in the individual's memory. Even after repeated drill, it will quickly fade beyond retrieval."

Arthur Jensen, Intelligence and educability