Portitor ratem per alveum ad alteram ripam agit.

Because portitor is in the nominative singular, the case normally used for the subject.

Here, portitor means the ferryman or boatman, and it is the one performing the action of agit. So grammatically, portitor is the person who is driving/steering.

Because ratem is the accusative singular form of ratis.

The verb agit takes a direct object: the thing being driven or steered. In this sentence, the ferryman is driving the boat/raft, so ratis has to appear in the accusative case:

• nominative: ratis
• accusative: ratem

So ratem shows what the ferryman is moving.

Agit is from ago, agere, a very common verb with a broad range of meanings such as drive, lead, set in motion, or do depending on context.

In this sentence, with a ferryman and a boat, agit means something like:

• drives
• steers
• guides
• propels

So it does not mean a vague does here. It has the more physical sense of moving something forward.

Grammatically, agit is:

• 3rd person singular
• present tense
• active voice
• indicative mood

So: he drives/steers.

They are accusative for a different reason from ratem.

• ratem is accusative because it is the direct object of agit
• alveum is accusative because it follows per
• ripam is accusative because it follows ad

In Latin, some prepositions regularly take the accusative case. Two of them are:

• per
  • accusative = through, along
• ad
  • accusative = to, toward

So:

• per alveum = through/along the channel
• ad alteram ripam = to the other bank

They express two different kinds of movement:

• per alveum tells you the path or route: through the channel / along the riverbed
• ad alteram ripam tells you the destination: to the other bank

So the sentence gives both:

1. where the boat moves through
2. where it ends up going to

That is a very common Latin pattern: one phrase for the route, another for the goal.

Because alter usually means the other of two, while alius means another or a different one more generally.

With a river, there are naturally two banks: this bank and the other bank. So ad alteram ripam is very natural Latin for to the other bank.

Also, alteram agrees with ripam:

• feminine
• singular
• accusative

That agreement is required because alteram describes ripam.

Because Latin adjectives agree with the nouns they describe in:

• gender
• number
• case

Here:

• ripam is feminine singular accusative
• alteram is also feminine singular accusative

So they belong together: alteram ripam = the other bank.

Even if the word order changed, the matching endings would still show the connection.

Because classical Latin does not have articles like English the and a/an.

Latin usually leaves that idea to context. So a noun like portitor can mean:

• a ferryman
• the ferryman

and ratem can mean:

• a boat/raft
• the boat/raft

The surrounding context or the translation will decide which sounds best in English.

It matters, but not in the same way it does in English.

Latin relies much more on endings than on word order, so the sentence could be rearranged without changing the basic meaning, for example:

• Portitor ratem per alveum ad alteram ripam agit
• Ratem portitor per alveum ad alteram ripam agit
• Per alveum portitor ratem ad alteram ripam agit

The endings still show:

• portitor = subject
• ratem = direct object
• alveum after per
• ripam after ad

That said, the chosen order is natural and clear. It presents:

1. the subject
2. the object
3. the route
4. the destination
5. the verb at the end

Putting the verb at the end is especially common in Latin prose.

A learner often wants to sort the forms by type:

• portitor: 3rd-declension noun, nominative singular
• ratem: from ratis, 3rd-declension noun, accusative singular
• alveum: from alveus, 2nd-declension noun, accusative singular
• ripam: from ripa, 1st-declension noun, accusative singular
• alteram: adjective agreeing with ripam, accusative feminine singular
• agit: from ago, agere, 3rd-conjugation verb, 3rd person singular present active

So this one sentence gives you examples from several major noun patterns plus a very common verb pattern.

Yes. Ratis can mean raft, and in some contexts it can also refer more loosely to a boat or small vessel.

Which English word is best depends on the context given in the lesson. Grammatically, though, nothing changes: ratem is still the direct object of agit.

Because per and in do different jobs.

• per
  • accusative emphasizes movement through or along
• in
  • ablative usually means in or on a place, more like position
• in
  • accusative can mean into

So per alveum focuses on the route the ferryman takes. It suggests motion through the channel itself, not just location in it.

That makes per alveum a good choice for a sentence about guiding a boat across.