The main objective of this work is to consider the relationships that, especially since the late nineteenth century, have maintained the theoretical linguistics and the commitment to create artificial languages, especially those intended to be used as auxiliary languages in the international sphere. We focus our attention on three outstanding figures of twentieth-century linguistics: O. Jespersen, E. Sapir and A. Martinet. Their interest in artificial languages should not be seen as a mere curiosity in their intellectual career, but is a direct reflection of his own thinking about language and a way to test some of the ideas that sustain it.