Ego credo nos in villa manere posse, quamquam pluvia frigida cadit.

Latin commonly uses an indirect statement after verbs of thinking/saying/knowing like credo. Indirect statement = accusative subject + infinitive:

• credo = I believe
• nos (accusative) = “that we” (subject of the infinitive)
• posse/manere (infinitives) = the reported verb(s)

Using quod + a finite verb is possible in later/less formal Latin, but the classic/default structure is accusative + infinitive.

Grammatically, posse is the key infinitive because it carries the idea to be able. manere is another infinitive that depends on posse:

• manere = to stay
• posse manere = to be able to stay

So the structure is “I believe (that) we are able to stay…”

Posse is the present infinitive of possum. Present infinitive in indirect statement usually represents action contemporary with the main verb (credo)—so “I believe (right now) that we can stay (now).”

If it were prior time, you might see potuisse (perfect infinitive: “have been able”), and for future time poturos esse (future infinitive: “will be able”).

Because in takes:

• ablative for location (in the villa → in villā)
• accusative for motion toward (into the villa → in villam)

Here it’s staying in a place (location), so villa is ablative: in villā.

Villa is a 1st-declension noun. In the ablative singular, it ends in -ā:

• nominative: villa
• ablative: villā

So in villā = in the villa / in the country house.

Quamquam means although and normally introduces a concession clause with the indicative in Latin (especially in straightforward prose):

• quamquam pluvia frigida cadit = “although cold rain is falling”

Latin tends to use subjunctive for other kinds of “although” clauses with different conjunctions (like cum, etsi can vary, quamvis often takes subjunctive), but quamquam commonly stays with the indicative.

Pluvia is the subject of cadit:

• pluvia (nominative singular) = rain
• cadit (3rd person singular) = falls / is falling

So literally, “cold rain falls,” i.e., “it’s raining cold rain.”

Frigida is an adjective modifying pluvia and agrees with it in gender, number, and case:

• pluvia = feminine, singular, nominative
• frigida = feminine, singular, nominative

So pluvia frigida = cold rain.

Latin word order is flexible because meaning is largely shown by endings. A common pattern is to keep closely related items together and place important words in emphatic positions:

• nos early makes clear who the embedded subject is.
• in villa sits next to manere because it belongs with “stay.”
• manere posse keeps the infinitives together.

Different orders are possible, but this one is very natural and readable.