Esperanto and Interlingua are two planned languages with different approaches to the problem of providing an International auxiliary language (IAL). Esperanto has many more speakers; the number of speakers is c. 100,000-2,000,000. On the other hand, the number of speakers is c. 1,500 for Interlingua, but speakers of the language claim to be able to communicate easily with the c. 1 billion speakers of Romance languages, whereas Esperanto speakers can only communicate among each other.
Although they are both classed as IALs, the intellectual foundations of Esperanto and Interlingua are quite different. Despite divergent theory, in practical terms, language usage in the two communities has sometimes shown convergences. It has been argued that each language is a successful implementation of a different particular IAL model. However, in both language communities there is a polemical tradition of using external criteria to critique the other (e.g., judging Interlingua by Esperantist criteria and vice versa).
