Medicus dicit puerum omnino sanum esse.

Because after dicit Latin uses an indirect statement construction, often called the accusative-and-infinitive.

In English, we say:

• The doctor says that the boy is completely healthy.

In Latin, instead of using that plus a finite verb, Latin often uses:

• a subject in the accusative +
• an infinitive

So puerum is the subject of esse, but because it is inside the indirect statement, it appears in the accusative rather than the nominative.

For the same reason: this is an indirect statement.

After verbs of saying, thinking, knowing, hearing, and perceiving, Latin often uses:

• accusative subject
  • infinitive verb

So instead of something like puer est sanus, the reported statement becomes:

• puerum ... sanum esse

This is Latin’s normal way of expressing that the boy is healthy after dicit.

Because sanum agrees with puerum.

Since puerum is masculine singular accusative, any adjective describing him inside the indirect statement must also be masculine singular accusative:

• puerum = masculine singular accusative
• sanum = masculine singular accusative

So sanum is not accusative because it is a direct object; it is accusative because it is an adjective agreeing with puerum.

It is an indirect statement made up of:

• puerum = subject of the infinitive, in the accusative
• sanum = predicate adjective agreeing with puerum
• esse = infinitive verb
• omnino = adverb modifying sanum or the idea of being healthy

So the whole phrase means something like the boy to be completely healthy, which English naturally turns into that the boy is completely healthy.

Because Medicus is the subject of the main verb dicit.

So the sentence has:

• Medicus = subject of the main clause
• dicit = main verb
• puerum omnino sanum esse = indirect statement depending on dicit

In other words, the doctor is the one doing the saying.

Omnino is an adverb meaning something like completely, altogether, or entirely.

Here it strengthens sanum:

• sanum = healthy
• omnino sanum = completely healthy / entirely healthy

So it is not describing dicit; it is describing the state of health.

Yes. Latin word order is much freer than English word order because the endings show the grammatical relationships.

For example, the following would still mean the same thing:

• Medicus puerum omnino sanum esse dicit.
• Puerum medicus omnino sanum esse dicit.
• Medicus dicit omnino puerum sanum esse.

Some orders may sound more natural or emphasize different words, but the basic meaning remains the same.

The given order is perfectly normal.

Because dicit here introduces an indirect statement.

With verbs like dico, an accusative followed by an infinitive is normally understood as:

• the accusative = subject of the infinitive
• not a separate direct object of the main verb

So puerum ... esse forms a unit: the boy to be ...

If puerum were just the direct object of dicit, we would expect a different structure and no infinitive like this.

Because in this kind of sentence Latin usually does not need one.

English commonly says:

• The doctor says that the boy is healthy.

Latin normally says:

• The doctor says the boy to be healthy
  that is, accusative + infinitive

So the idea of English that is built into the indirect statement construction rather than expressed by a separate word.

Yes. Dicit is present active indicative, third person singular, from dico.

It means he says or the doctor says.

Breaking it down:

• dic- = verb stem
• -it = third person singular present ending

So Medicus dicit means the doctor says.

Usually no, not in standard Latin prose here.

In some languages, forms of to be can be left out, but in Latin indirect statement this infinitive is normally expressed:

• puerum sanum esse

Without esse, the structure would be incomplete or at least nonstandard in ordinary prose.

They would both be nominative, because they would belong to a normal main clause rather than an indirect statement.

Direct statement:

• Puer omnino sanus est.
  = The boy is completely healthy.

Reported after dicit:

• Medicus dicit puerum omnino sanum esse.

So one useful pattern to remember is:

• direct statement: nominative + finite verb
• indirect statement: accusative + infinitive

Grammatically, esse is an infinitive, so literally it is to be. But inside an indirect statement, English usually translates it with a normal finite verb:

• literal Latin structure: the boy to be healthy
• natural English: that the boy is healthy

So in form it is to be healthy, but in sense it corresponds to is healthy in reported speech.

The key point is the Latin indirect statement:

• after a verb like dicit
• Latin often uses accusative subject + infinitive
• adjectives inside that clause agree with the accusative subject

So in this sentence:

• Medicus = nominative subject of the main verb
• dicit = main verb
• puerum = accusative subject of the indirect statement
• sanum = adjective agreeing with puerum
• esse = infinitive
• omnino = adverb meaning completely

This is one of the most important and common Latin constructions.