"You throw very many fish onto the floor."
Translation:Tu plurimos pisces in pavimentum iacis.
Yes: to indicate the two phrases mean two different things.
in pavimento means: on the floor. Location. Static.
in pavimentum means: onto the floor. Action. A fish temporarily in flight...
Latin is quite particular. Supposedly, this was why European statesmen long liked to have treaties, etc., written in Latin, as it avoided deliberate or accidental ambiguities that might occur in the vernacular languages.
French was also the treaties language and the diplomacy language, but later, as it's also a very precise language (they say. Maybe because of its very strict grammar).
You raise an interesting point, bonnythedog. Although rich in demonstratives (proximal, medial, distal), the lack of definite and indefinite articles in classical Latin could cause problems for precision, and helps explain the gradual use of unus (indefinite) and ille & ipse (def) respectively for those purposes in Late Latin (and even sometimes in classical Latin, as with Cicero's rendering of Plato's Timaeus), which of course became fully developed in the Romance languages over time. As Late Latin developed a different type of precision with those articles, the precision of the classical Latin declension system began to decline (Romanian is the only Romance language that retains cases), and we see a loss of the distinction between long and short vowels (poetic meter is on the wane in Late Latin, although there is a forma mixta) and a greater abundance of prepositions. These changes were gradual, of course, so if one studies Late Latin vis-à-vis the emerging Romance languages of the 9th - 11th centuries there is still some use of cases. Cf. Solodow, Latin Alive. The Survival of Latin in English and the Romance Languages (Cambridge, 2010) esp. 239-40; Mario Pei, The Story of Latin and the Romance Languages (New York, 1976).
Alas this is not done snymore. I experienced this when I was militsry UN observer in the Middle East. The armistice agreement was written in French and English and bothe versions had been declared equal. When there was a problem, the Arabs used the French because it is more exact, and the the Israeli's came with a clever legal adviser who pointed out that some English word could also be explained in a different way.
Late reply, but including the nominative personal pronouns (tu, vos, ego, etc.) is usually done either for clarity or for emphasis. Consider the following:
"Psittacum ebrium pulsas" - You hit the drunk parrot. Just a statement of fact.
"Tu psittacum ebrium pulsas" - YOU hit the drunk parrot. Now we're emphasizing that it was you (and not someone else) that abused this poor bird.
The noun piscis is what is termed an i-stem noun, and according to Allen and Greenough's Latin Grammar's page on 3rd declension: summary of I-stem forms,
The i-declension was confused even to the Romans themselves, nor was it stable at all periods of the language, early Latin having i-forms which afterwards disappeared. There was a tendency in nouns to lose the i-forms, in adjectives to gain them.
So I believe there is no difference in usage or meaning; the is ending is an earlier form which later changed to es. Though both may still be encountered in original texts, the es ending is now generally taught as standard.
Plurimes does not exist in Latin so far as I know. It is plurimos, with -os, because this is the ending for the accusative masculine plural of the second declension.
Declension of plurimus (second declension, masculine):
The fish is the thing the verb action is being done to so it is in the accusative plural form. An adjective must match with the noun it modifies in gender, number, and case. Plurimos is the masculine accusative plural form of the adjective.
Plurimi is never accusative so cannot be used with pisces here. It can when pisces is the nominative case, when the fish are doing the action. Plurimi pisces natant -> 'Very many fish swim'.