Histrio speciem mutat.

Because histrio is a third-declension noun, not a second-declension noun. In Latin, the subject is usually in the nominative case, and the nominative singular of this word is histrio.

Its dictionary form is histrio, histrionis. So in this sentence, histrio is simply the nominative singular subject: the actor or the performer.

Speciem is accusative singular. It is the direct object, the thing being changed.

The dictionary form is species, speciei, a fifth-declension noun. In the accusative singular, species becomes speciem. So speciem means appearance as the object of the verb.

Mutat is third-person singular, present active indicative of mutare.

That means:

• present = happening now or generally true
• active = the subject does the action
• indicative = a normal statement
• third-person singular = he/she/it

So mutat means changes or is changing, depending on context.

Because Latin usually does not need an explicit subject pronoun when the verb ending already shows the person and number.

Here, the -t in mutat already tells you the subject is he/she/it. So Latin can simply say Histrio speciem mutat without adding a separate word for he.

If a pronoun were added, it would usually be for emphasis.

Latin word order is much more flexible than English word order because Latin uses case endings to show what each word is doing.

A very common Latin pattern is:

• subject
• object
• verb

So Histrio speciem mutat is a very normal Latin order. English usually prefers The actor changes appearance, but Latin often likes to place the verb later, especially at the end.

Yes. Latin could also say things like:

• Speciem histrio mutat
• Mutat histrio speciem
• Speciem mutat histrio

The basic meaning would stay the same, because the endings still show the grammar:

• histrio = subject
• speciem = direct object

What changes is mostly emphasis and style, not the core meaning.

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

So:

• histrio can mean the actor or an actor
• speciem can mean the appearance or an appearance

You decide which English article to use from the context.

Yes. The Latin present tense often covers both ideas.

So mutat can be translated as:

• changes
• is changing

English makes a stronger distinction between simple present and progressive present than Latin does.

A learner would normally memorize these forms:

• histrio, histrionis — actor, performer
• species, speciei — appearance, form, look
• muto, mutare, mutavi, mutatum — change, alter

Learning the dictionary forms helps you understand why the sentence uses:

• histrio for the nominative subject
• speciem for the accusative object
• mutat as the finite verb

Because species is the nominative form, while speciem is the accusative form.

Since the word is the direct object of mutat, Latin puts it in the accusative:

• nominative: species
• accusative: speciem

So the sentence needs speciem, not species.