In the following sentence : "Bref, ce mélange unique de similitudes et de divergences, ainsi que mon désir de renforcer ma maîtrise de la langue espagnole, m'a toujours motivé à découvrir votre pays."
Should I replace the m'a with m'ont, since I'm talking about two distinct elements?
Original answer:
I think you should make the agreement. Since there are two elements mentioned (mélange and désir), you should use "m'ont" to agree with the plural subject. The correct sentence in my humble opinion would be:
"Bref, ce mélange unique de similitudes et de divergences, ainsi que mon désir de renforcer ma maîtrise de la langue espagnole, m'ont toujours motivé à découvrir votre pays."
New Edit (25/01/2024) following the comments and this content:
Note that there is a debate regarding the agreement here. Some argue for a singular agreement with 'ce mélange' as the main subject, while others advocate for a plural agreement due to the presence of two distinct elements. Both forms may be considered grammatically acceptable, and the choice may depend on the interpretation of the relationship between the main subject and the ainsi que clause. More specificaly,
Singular Agreement (m'a): The argument here is that the singular agreement may be justified because the main subject is "ce mélange" (this mixture), which is singular. The ainsi que clause might be seen as a parallel construction rather than combining with the main subject to form a plural subject.
Plural Agreement (m'ont): The argument in favor of the plural agreement suggests that since there are two distinct elements mentioned (mélange and désir), it makes sense to use the plural form to agree with the combined subjects.
Hence,
Bref, ce mélange unique de similitudes et de divergences, ainsi que mon désir de renforcer ma maîtrise de la langue espagnole, m'a/m'ont toujours motivé à découvrir votre pays.
In this particular sentence, I believe the verb can only be in the plural. According to my favorite Grevisse (Le français correct, 1984):
(985) Subjects linked by AINSI QUE, COMME, AVEC, etc.
a) If the conjunction is copulative ( = aggregates subject elements), the verb agrees with the whole: Le français ainsi que l'italien DÉRIVENT du latin (Littré). - Aussi bien l'oncle Mathieu que tante Philomène n'ÉTAIENT pour moi que sons (H. Bosco). - La voix non plus que la silhouette ne lui ÉTAIENT connues (A. de Châteaubriant). - Le murmure des sources avec le hennissement des licornes se MÊLENT à leurs voix (Flaubert). - L'une comme l'autre GARDENT peu de loisir disponible pour l'aventure (M. Prévost). - Tant le sol boueux que l'eau m'ÉTAIENT présents (H. Bosco).
b) If the conjunction clearly puts the elements in comparision, the agreement is with the first element:
Le français, ainsi que l'italien, DÉRIVE du latin (Littré). - Son visage, aussi bien que son cœur, AVAIT rajeuni de dix ans (Musset). - Le manque d'air ici, autant que l'ennui, FAIT bâiller (A. Gide). - L'un comme l'autre EST pris au jeu (Id.). - La religion, comme la politique, A ses Brutus (A. Hermant). - Renée, pas plus que Gilbert, n'ÉTAIT retournée chez les Guillaume (M. Arland).Same (with AVEC), if one element is clearly accessory to the other:
Le travail avec ses servitudes lui INSPIRA de bonne heure un grand dégoût (M. Garçon).
In the present case, the mix of similitudes & divergences neither approaches nor opposes the desire to master the language; they are just two juxtaposed, separate incentives. The conjunction is copulative in meaning, not comparative, whence:
... m'ont toujours motivé.
(Edited after jlliagre's comments)
Disclaimer. My approach is descriptive not prescriptive, maybe I should add this to my SE profile. I am not a party in any effort at normalizing French, only explaining how I write it.
In particular, I write w/o regard to the ongoing normalization process. I guess it systematically moves towards relaxing the rules I follow, not toward invalidating them; I have not checked though. End of disclaimer.
Back to the question at hand: on the prescriptive side and as far as I know (which need not include the latest news, see above), school teachers are now instructed to accept both singular and plural in every instance, as reflecting the 2 equally valid intents of the writer.
Finally, I will add a word about commas. Grevisse's examples clearly show they are optional and somehow related to the chosen agreement: his editors, if noone else, prefer them with the singular. However, he has not a word about them in the entire section I quoted, so I believe the subject is quite distinct.
My own opinion is, punctuation comes after deciding the contents of the text and the comma basically marks where speakers pause; if they help silent readers (which they certainly do, so typesetters and editors will inevitably have their say about this), it is secondary.
