Less explicable is Spanish he, from Latin habeo "I have," as the loss of the final -o is unexpected and Penny (2002) concludes was due to apocopation by analogy with words like buen and mal.

Following Meyer-Lübke (1890), Old Spanish fere and its dialect variants in fer point to a stress variant in Vulgar Latin *facére that reduced to *fére while modern Spanish hacer reflects Vulgar Latin *fácere > *fácer and then remodeled to hacér in the Middle Ages. While an argument from stress variation in Vulgar Latin should raise eyebrows, it has at least one strong case in pero / peró. A further case that Vulgar Latin *fácere existed is in Old Catalan far "to make," from a pre-form *fare that must derive from a stress-heavy /a/ that caused syncopation of the interior -e-. See Rufat (2013) for further discussion from a Catalan perspective; Chambon (2013) for additional remarks.

The Dictionnaire Étymologique Roman takes a different approach, reconstructing all of the above words in a single Proto-Romance etymon, */ˈɸak‑e‑re/, except for Old Spanish far, which reflects Proto-Romance */ˈɸ‑a‑re/.

In the 3rd or 4th cent. text Appendix Probi we find the line: fames non famis "[the word for 'hunger' is] fames, not famis." The author's spelling correction proves how the word was pronounced by common speakers, and offers a rare glimpse of the evolution of Latin into Romance languages such as Spanish.

Words for hunger tended to be borrowed into Indo-European languages or internally innovated. "There is only one word reconstructed in Proto-Indo-European that means 'hunger' (a Hittite-Tocharian isogloss) and even this is problematic in tha a comparison between Hit kāst- 'hunger' and Toch B kest 'hunger' still only yields a PIE *Kos-t-, i.e. we can only say that the word begins with a velar but must be uncertain which velar that is (it could be *ges- for example)." ~ Mallory & Adams, The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World (2006)

Borrowing of prepositions is a rare phenomenon, and the variety of different written forms in Old Spanish is troublesome. To explain how the different written forms arose from Arabic, Ford (1911) distinguishes Old Spanish fasta from ata and fata. Ata and fata, Ford explains, are more conservative borrowings from Arabic ḥattā; later, an s intruded into fata to give us fasta. Between the three words fasta alone survived, and evolved into hasta.

But is an "intrusive s" a satisfying answer? Corriente's (1983) answer is that Old Spanish speakers also utilized the Latin phrase ad ista "to this" as a preposition, and it influenced the evolution of fata by transferring its -s-. For the continued etymologies of these words, see a and éste respectively.