This paper deals with the middle diathesis in the Romance languages and the importance of defining this category for the teaching. So far in the teaching the practical grammar the middle voice, or the middle diathesis, is mentioned only referring to the pronominal verbs, but not to the Romance Perfects with "to be" as auxiliary verb. The importance of the notion of the middle voice for the language teachers is that it allows to explain more satisfactorily some difficulties of the practical grammar. One of this difficulties is the use of alternating pronominal verbs, that is, where the reflexive pronoun can be used or not, such as morir - morirse. Another difficulty is the existence of two types of verbs in the Passato prossimo (Italian) and Passe Compose (French): the auxiliary verb avere (avoir) and essere (etre). Although only academic grammars mention the middle voice, and practical grammars generally ignore it, in modern Spanish (as in many other languages) its presence is unquestionable. That is why some of the Spanish verbs have the reflexive forms that can mean the same as the active one. The vestiges of the middle voice in modern Indo-European languages are clearly visible, when we compare the old deponent verbs of Latin with their Spanish derivatives. We can observe that in its majority there is a duality of forms, active and pronominal. Many times, the reflexive forms are more colloquial or humoristic, and active forms are more serious and literary. Another problem in the teachings of pronominal verbs is the confusion of "se" in Accusative and "se" in Dative. Insofar as the middle diathesis does not have in Spanish some regular formal expression, it acquires sometimes active forms, ad sometimes, alternating pronominal forms. The middle voice does not include the verbs with the Dative Reflexive, however sometimes the reflexive with Accusative and the reflexive with Dative are confounded. The perfects with essere in Italian, etre in French and ser in medieval Castilian belong to the middle diathesis. Analyzing the semantics of thus, we see that the verbs of the main events of life also belong to the middle voice. In addition, the verbs of motion in many cases belong to the middle diathesis too, and this involves the idea that the Indo-European languages conserve in their structure the reflex of belief that the movements of people are not as deliberate as believed. The middle diathesis, which is common for the verbs of state and the verbs of movement, suggests that they can occur due to the incontrollable forces.