All these words can be used as invective against someone thought to be stupid or foolish. Moron , imbecile and idiot formerly functioned neutrally as classifications for degrees of mental deficiency, moron denoting a mild deficiency, imbecile a moderate level of deficiency, and idiot a degree of severe deficiency. Nowadays the phrase "mentally retarded child" (or person) preceded by a qualifying word such as mildly or severely is the preferred term, both in popular and technical writing, for any of these levels. As invective, little distinction exists between the three terms.

Dullard and simpleton both lack the precise denotations of the previous group, but they do refer to a slow-witted rather than a foolish person. Dullard is the more formal of the two and suggests a mild degree of mental deficiency that renders one passive, unresponsive or imperceptive: appalled to find that her class seemed to be filled with dullards . Simpleton suggests greater deficiency; it has a faintly archaic flavour that sometimes brings to mind a touching innocence or sweetness of disposition: the class simpleton whom we all loved for his good nature despite his inability to learn.

The remaining words are all extremely informal. Clot suggests someone prone to making foolish mistakes: such a clot that he gave his intending visitors the wrong address. As in the case of many colloquial terms, other words exist with varying currency but the same generality of meaning. Thus, instead of clot , we may hear words like dill , dimwit , nong , twerp , etc. Except for its much greater informality, dope is like dullard ; but, as used, it suggests ill-advised or foolish behaviour rather than mental deficiency: a dope to try swimming against such an undertow. Numbskull must once have seemed a vivid coinage, but now, through over-use, it has faded somewhat as a term for a hopelessly stupid person: numbskulls who leave school before their final exams.