Learn Hardcore Latin: Hospes cum domina sedet et fructus dulces in mensa videt. - The guest sits with the lady of the house and sees sweet fruits on the table.

Hospes can mean either guest or host in Latin. Context decides which is intended.
In this isolated sentence, you only know that hospes is some kind of person involved in hospitality. Many textbooks gloss it as guest, so unless the wider context says otherwise, guest is a safe default.

Grammatically:

hospes is nominative singular, so it is the subject of sedet and videt.

Why is domina in that form, and what does cum domina mean literally?

Domina is in the ablative singular (same form as the nominative for a‑stem nouns, but here used with a preposition).

cum is a preposition that takes the ablative.
cum domina literally means with the lady / with the mistress.

This is the standard ablative of accompaniment: it shows with whom the subject is doing something. So hospes cum domina sedet = the guest sits with the lady.

What tense and person are sedet and videt, and how do they relate to hospes?

Both sedet and videt are:

3rd person singular
present tense
indicative mood
from sedēre (to sit) and vidēre (to see).

They agree with hospes (a singular subject). So:

hospes … sedet = the guest sits
hospes … videt = the guest sees

The et in the middle connects the two verbs with the same subject:

hospes … sedet et … videt
the guest sits and sees

Why is domina not also the subject of sedet and videt? Could it mean “the guest and the lady sit and see…”?

No, domina is not a second subject here because:

It is governed by cum → cum domina (ablative), not plain nominative domina.
cum + ablative expresses accompaniment, not a second subject.

So the structure is:

Subject: hospes
With whom: cum domina (ablative of accompaniment)
Verbs: sedet and videt

Meaning: The guest sits with the lady and sees sweet fruits on the table.
If Latin wanted the guest and the lady sit, you’d typically see hospes et domina sedent (both in nominative, plural verb).

Why is fructus in that form, and is it singular or plural?

Fructus belongs to the 4th declension. Here, it is:

Accusative plural masculine

4th‑declension masculines have ‑ūs in the nominative singular and ‑ūs in the accusative plural. Context and agreement tell you which is which:

It comes after videt (a verb that can take a direct object).
It is modified by dulces, which is accusative plural masculine.

So fructus dulces = sweet fruits (direct object), not sweet fruit (subject).

Why is dulces used and not dulcis?

Dulcis, dulce is a 3rd‑declension adjective. It must agree with the noun it modifies in:

Gender: masculine (because fructus is masculine)
Number: plural
Case: accusative

The form that matches fructus (accusative plural masculine) is dulcēs (spelled dulces here). So:

fructus dulces = sweet fruits (plural direct object)

If it were singular direct object, you’d have fructum dulce.

Why is in mensa translated as “on the table” and not “in the table”?

Latin in with the ablative usually means in or on as a location (where?), without movement:

in mensā (ablative) = in/on the table (location)

Which English preposition you choose, in or on, depends on what is natural in English for that noun. We say:

on the table, not in the table, so in mensa is translated on the table.

If there were movement into the table, Latin would use in + accusative (e.g. in mensam = onto the table).

Why does in take the ablative here? When would it take the accusative instead?

In is a preposition that can take:

Ablative → shows location / rest (where?)
- in mensā = on/in the table (no movement, just location)
Accusative → shows motion towards / into (where to?)
- in mensam = onto/into the table

In this sentence the guest sees fruits already on the table, so it is a static location → ablative (mensa).

Does Latin have words for “the” and “a” in this sentence? How do I know whether to translate hospes as “the guest” or “a guest”?

Latin has no separate words for the or a/an. Nouns usually appear without articles:

hospes can be guest, a guest, the guest
domina can be lady, a lady, the lady
mensā can be table, a table, the table

You choose the vs a based on context and natural English style. Many textbook sentences default to the (e.g. the guest sits with the lady), but a guest is equally possible without broader context.

Why is the word order Hospes cum domina sedet et fructus dulces in mensa videt and not like in English?

Latin word order is flexible because case endings show each word’s role. A common neutral pattern is Subject – other elements – Verb. In this sentence:

Hospes (subject)
cum domina (with whom)
sedet (verb 1)
et fructus dulces in mensa (object + where)
videt (verb 2)

Latin often puts verbs near the end, but coordinating two verbs with et lets each one sit near its own phrase:

hospes cum domina sedet
(hospes) fructus dulces in mensa videt

If you shuffled some pieces (e.g. Hospes sedet cum domina et videt fructus dulces in mensa), it would still be grammatical Latin with the same basic meaning. The endings, not the order, do the heavy grammatical work.