Latin was a language which predominant order was Subject-Object-Verb, as in the example proverb Errare Humanum Est
So, why all its modern descendents are predominantly Subject-Verb-Object order? Or are there some that I don't which order is not that?
I can assert the SVO order on Portuguese, Spanish, Catalan, French, Italian and Romanian, which are the most represented in Europe. May be there is some not so popular language that is not SVO.
The premise holds for most Romance languages but it is difficult to categorize Spanish (the largest latin language by number of speakers) as an SVO language. The earliest texts in medieval Spanish were all VSO and I, as a native Spanish speaker, tend to use VSO sentences slightly more often than SVO.
I will say "Ya ha llegado Jose a casa" (already has arrived Joe home) much more commonly than "Jose ya ha llegado a casa" (Joe already has arrived home) for example which sounds slightly clumsy.
Even when encapusaled within a subjunctive sentence (Quiero que venga Jose) the verb preceeds the object which sounds very alien to a French or Italian speaker for example - you would never say "Je veux que vienne Jose").
VSO sentences however are actually totally forbidden in Italian and French. They simply don't exist. French is the most strictly SVO language, followed by Italian. The least strict is Spanish where all sentence orders are allowed except SOV.
Why is this the case? Hard to say. Possibly Arabic influence on Spanish which has a similar flexibility between VSO and SVO. After all Castilian Spanish was partly built on the Mozarabic dialect of Kingdom of Toledo - a region where Christians were bilingual even for a good two centuries after its reconquest.
It is a superstition to think that all languages are predominantly SOV, SVO, VSO or some other combination of these hieroglyphs. This is not true of Latin, and certainly not true of ancient Indo-European languages like Sanskrit or Avestan, where the word order is almost completely free.
As TKR has very rightly pointed out, the “proverb” “errare humanum est” is not an example of SOV because humanum is not an object but a predicate adjective. By the way, this “famous proverb” is not actually quoted by any ancient author; the oldest attested version of it is in St Augustine of Hippo, who in fact wrote “humanum fuit errare”, so: predicate + verb + subject.
This said, I would actually agree that in the modern Romance languages the usual sequence is SVO. In cases like “je t’aime” one could argue that “t(e)” is not a direct object but part of the verb complex; it is not a word in its own right. We also say things like “Toi je t’aime”, which you might want to analyse as OSOV, though I would analyse it as topic + (clitic+clitic+verb). Neither “je” nor “te” can be used as an isolated statement in French. The response to the question “Whom do you love?” is not “te” but “toi”.
