Postea figulus dicit se aliud vas cras fingere posse, si lutum bonum habeat.

After verbs like dicit, Latin usually does not use a separate word for English that. Instead, it often uses the accusative-and-infinitive construction, also called indirect statement.

So dicit se aliud vas cras fingere posse is literally something like he says himself to be able to shape another vessel tomorrow. In normal English, we translate that as he says that he can make another vase tomorrow.

Se is the accusative subject of the indirect statement. In Latin, the subject of a reported statement goes into the accusative.

It is specifically se because it refers back to the subject of the main verb, figulus. So the sentence means that the potter says that he himself can do it.

If it referred to some other male person, Latin would more likely use eum instead.

Because the whole reported statement is being put into infinitive form after dicit.

Within that reported statement, posse is the main idea: to be able. But posse itself normally takes another infinitive to explain able to do what? That is where fingere comes in.

So:

• posse = to be able
• fingere = to shape / make

Literally, the structure is he says himself to be able to make another vessel tomorrow.

Aliud vas is accusative singular neuter. It is the direct object of fingere.

The potter is making or shaping another vessel, so that noun phrase has to be in the accusative.

Also:

• vas is neuter singular
• aliud agrees with it in gender, number, and case

A small detail that can confuse learners: for neuter nouns, the nominative and accusative are often identical in form, and vas is one of those cases.

Alius usually means another or a different one.
Alter more often means the other of two or a second one.

So aliud vas is a natural way to say another vessel in a general sense. If the context were specifically about two vessels, alterum vas might be more pointed.

No. Si does not always take the subjunctive. Very often it takes the indicative.

Here, habeat is best understood as a subjunctive because the if-clause is part of the potter’s reported words or thought. In Latin, subordinate clauses inside indirect discourse are often drawn into the subjunctive.

So si lutum bonum habeat means something like:

• if he has good clay
• or a bit more literally, if he should have good clay

Because the main verb is dicit in the present tense, the subjunctive here is also present: habeat.

Posse is a present infinitive, and in indirect statement that usually shows time contemporary with the main verb dicit.

So the basic idea is:

• he says now
• that he is able or can
• to make another vessel tomorrow

The future time is supplied by cras, not by making posse future. Latin often leaves the infinitive present when the time reference is already clear from another word.

Cras means tomorrow, and it modifies the action of fingere.

So it tells us when the making will happen:

• se aliud vas cras fingere posse = that he can make another vessel tomorrow

It does not go with dicit. The meaning is not tomorrow he says, but he says ... that tomorrow he can make.

Latin word order is much freer than English word order because the endings show how the words function.

This sentence is arranged quite naturally:

• Postea sets the scene: afterwards
• figulus dicit gives the main statement
• then comes the reported content
• and the si clause comes at the end

You could move some words around, especially cras, without changing the core meaning. But the current order is smooth and idiomatic.

Yes, they are related in sense and probably helpful to learn together.

• figulus = potter
• fingere = to shape, mold, form

That makes good contextual sense: a potter is someone who shapes clay. Seeing the connection can make the vocabulary easier to remember.

A rough direct version would be something like:

Postea figulus dicit: cras aliud vas fingere possum, si lutum bonum habeo.

In the reported version:

• possum becomes posse
• the subject becomes se
• and the conditional clause may be shifted into the subjunctive, giving habeat

So the sentence is a good example of how Latin turns direct speech into indirect speech.