Puer corticem arboris tangit et rogat cur cortex quercus tam asper sit.

They are two forms of the same noun: cortex, corticis = bark.

• corticem is accusative singular, because it is the direct object of tangit: the boy touches the bark.
• cortex is nominative singular, because it is the subject of sit: the bark is rough.

So the change is caused by the noun’s job in each clause.

Because both are genitive singular forms. The genitive often shows possession or close relationship, and in English we often translate it with of.

• corticem arboris = the bark of the tree
• cortex quercus = the bark of the oak

So here the genitive tells you what the bark belongs to.

Because quercus is a 4th-declension noun. Its nominative singular and genitive singular are spelled almost the same if macrons are not shown.

With macrons, the forms are:

• nominative: quercus
• genitive: quercūs

In many beginner texts, macrons are omitted, so both appear as quercus. You identify the case from the grammar of the sentence.

Because cur cortex quercus tam asper sit is an indirect question after rogat.

Latin normally uses the subjunctive in indirect questions, so:

• direct question: Cur cortex quercus tam asper est? = Why is the bark of the oak so rough?
• indirect question: rogat cur cortex quercus tam asper sit = he asks why the bark of the oak is so rough

So sit is the present subjunctive of esse.

Cur means why. It introduces the question.

In this sentence, it introduces an indirect question because it depends on rogat:

• rogat = he asks
• cur ... sit = why ... is

So cur is the question word that starts the clause being asked.

Because asper agrees with cortex.

Adjectives in Latin must agree with the noun they describe in:

• gender
• number
• case

Here cortex is masculine nominative singular, so the adjective is also masculine nominative singular: asper.

That is why we get cortex ... asper sit = the bark ... is rough.

Tam means so. It modifies the adjective asper.

So:

• asper = rough
• tam asper = so rough

It adds emphasis: not just rough, but so rough.

Latin has no articles. It does not have separate words that exactly match English the and a/an.

So a noun like puer can mean:

• a boy
• the boy

The context tells you which is best in English. The same is true for cortex, arbor, and quercus.

You know from the case ending, not just from position.

• puer is nominative singular, so it is the subject of tangit and rogat
• corticem is accusative singular, so it is the object of tangit

Latin word order is more flexible than English because these endings show each word’s function. Even if the order changed, the cases would still tell you who is doing what.

Both are 3rd person singular present active indicative verbs.

• tangit = he/she touches
• rogat = he/she asks

Since the subject is puer, we translate them as:

• the boy touches
• and asks

The ending -t is the normal 3rd person singular ending in the present tense.

It has two main parts:

1. Puer corticem arboris tangit

   • Puer = subject
   • corticem arboris = object phrase
   • tangit = verb

2. et rogat cur cortex quercus tam asper sit

   • et rogat = and asks
   • cur cortex quercus tam asper sit = an indirect question

So the sentence is basically:

• main clause: the boy touches the bark of the tree
• main clause + indirect question: and asks why the bark of the oak is so rough