A few days ago an acquaintance asked a question concerning the history of Spanish and I thought maybe someone here knew something about it. The question is Why are the preterit(e) forms of ser and ir (fui, fuiste, fue, etc...) the same? Is there any historical reason/explanation?

This may answer your question:

"QUESTION: Why do ser and ir have the same form in the preterite?

First, it is really the perfect (= Spanish preterite) conjugation of the Latin verb ESSE "to be" which came to be used for both ser and ir in Spanish. In Spoken Latin, the preposition IN (> Spanish en) used with a location came to mean "movement toward". Also, ser and estar did not have the same restrictions in Old Spanish that they do in modern Spanish and consequently ser occurred at times where one might expect estar. Thus FUERUNT IN CAMPUM, for example, originally meant "they were at the countryside", but later "they were moving/in route toward the countryside", and eventually came to mean "they went to the countryside". Therefore, this paradigm, fui, fuiste, etc., eventually became associated with the infinitive ir "to go"."

http://www.virginia.edu/cla/avd/doc/spanish_history.html

Wow, :eek: very good explanation

Great find Felipe! Thanks for that. :)