For example, how would one translate the prepositions in the following phrases: "The man is like a dog" or "We go many places, such as the forum"? What case would "canis" and "forum" be, respectively? I've tried looking in quite a few places, but haven't found anything that matches these kinds of uses involving nouns. I assume the first example is just a verb and "canis" would be accusative, but for the second phrase I have no clue where to even start.
Thanks.
If you check the example sentences at Glosbe (https://glosbe.com/en/la/such%20as and https://glosbe.com/en/la/like) it seems that you could use any of the following for 'like' in the sense of equivalence or similarity: ut, uti, sicut, sicuti, velut, veluti, quasi (and I'd add tony's suggestion tamquam), all with the nominative, or similis with the dative. So it would be: "Homo ut (etc.) canis est", or "homo similis cani est".
It seems that (sic/vel)ut(i) can also be used for 'such as' or 'like' when giving an example (but not quasi or tanquam). So: "In multa loca imus, ut (etc.) in forum" (I'd repeat the preposition).
(Looking over the other answers that have been submitted, I see that most of this has already been covered there. Still, there may be some value here, since I've included attestations.)
1. The man is like a dog.
For a simple statement of similarity, of the sort 'x is like y,' I think the best approach is to use the adjective similis + dative, as in Pliny the Younger, Epistulae 8.21.5:
delicatus ac similis ignoto est, qui amici librum bonum mauult audire quam facere.
He is self-indulgent and like an ignoramus, who would rather listen to the good book of a friend than help produce it.
This would give Homo similis cani est.
For more complex statements of similarity, where you're saying, not simply 'x is like y,' but 'x does y like (i.e., in just the same way as/in the manner of) z,' an adverb like velut(i) can be used. An example is found in the opening of Sallust's Bellum Catilinae (1.1):
omneis homines, qui sese student praestare ceteris animalibus, summa ope niti decet, ne vitam silentio transeant veluti pecora, quae natura prona atque ventri oboedientia finxit.
All men who are eager to surpass all other animals should try with all their might not to pass their life in obscurity like cattle, which nature has fashioned face-down and slaves to their stomach.
Additionally, because Latin adjectives in the nominative (and also accusative) are often used where English prefers an adverb, similis can also be used for these statements, as in Pliny, Epistulae 8.14.24:
sed quid ego similis docenti? cum discere uelim, an sententias diuidi an iri in singulas oportuerit.
But why do I speak/write like someone giving a lesson, when what I want is to learn whether it was fitting that the proposals be divided or taken on individually?
2. We go many places, such as the forum.
One way to give examples that involve single words or phrases (as opposed to clauses), is once again to use velut(i), as in Quintilian, Institutio oratoria 2.21.8:
sed neque infinita est, etiamsi est multiplex, et aliae quoque artes minores habent multiplicem materiam, uelut architectonice (namque ea in omnibus quae sunt aedificio utilia uersatur) et caelatura, quae auro argento aere ferro opera efficit.
...and other lesser arts also have varied material, such as architecture...and engraving....
This would give In multa loca imus, velut (in) forum.
ADDENDUM: 7/6/2020:
As always, while looking for something else: Allen & Greenough p.384 (using adjective par, paris = equal; fair; fit [Oxford]):
"si parem sapientiam habet ac formam (Plaut. Mil. 1251). =
"If he has sense equal to his beauty (like his beauty).
Original Answer:
Try of "tamquam" (adverb) = "just as"; "just as if" (Pock. Ox. Lat. Dict.).
After reading about the murder of Rome's last great general, Flavius Aetius (he checked the advance of Atilla, for example), by feckless Emperor, Valentinian III, in 454, I found the response of Appolinarus who said to Valentinian: "Caeser, I know not your motivations or provocations, I only know that you have behaved just like a man who has cut off his right arm, with his left."
I translated this to:
"Caeser, provocatias vel causas tuas nescio, sed tamquam virum tu gessisti, qui cum sinistro bracchio dextrum secavisse, solum scio."
Unable to find the original Latin, and long before there was a Latin Stack Exchange, I e-mailed Prof. Lansford (Author of "The Latin inscriptions of Rome"), specifically about the "you-have-behaved-just-like-a-man-who" part.
The Professor was good enough to reply, confirming that "te gessisti tamquam virum qui" followed by accusative-infinitive form in indirect discourse, is indeed correct.
The noun instar in the ablative case with a genitive object can be used almost exactly like the English preposition "like". See here.
The biggest difference between "like" and instar is that "like" is extremely common in English, but instar is not nearly so common in Latin. So use instar, but don't overdo it. :)
Instar canis, like a dog.
Instar fori, like the forum.
