La leva attiva il meccanismo.

Because leva is a feminine singular noun in Italian, so it takes the feminine singular definite article la.

• la = the for feminine singular nouns
• il = the for masculine singular nouns

So:

• la leva = the lever

A lot of Italian nouns ending in -a are feminine, and leva is one of them.

Meccanismo is a masculine singular noun, so it takes the masculine singular definite article il.

• il meccanismo = the mechanism

This is a very common pattern:

• il
  • masculine singular noun beginning with most consonants
• la
  • feminine singular noun beginning with most consonants

Since meccanismo begins with m, il is the normal article.

Italian uses articles very regularly, often more regularly than English does. In this sentence, both nouns are specific:

• la leva = the lever
• il meccanismo = the mechanism

So the articles are completely natural and expected. In many cases, leaving them out would sound incomplete or ungrammatical.

Here, attiva is a verb: the third-person singular present form of attivare.

• attivare = to activate
• attiva = he/she/it activates

So:

• La leva attiva il meccanismo.
• The lever activates the mechanism.

This can confuse learners because attiva is also the feminine form of the adjective active. But in this sentence, it is clearly functioning as the verb because it sits between the subject and the object:

• La leva = subject
• attiva = verb
• il meccanismo = object

Italian verbs are usually learned in the infinitive form, and many infinitives end in -are, -ere, or -ire.

Here:

• attivare = to activate

In the present tense, an -are verb like attivare changes like this:

• io attivo = I activate
• tu attivi = you activate
• lui/lei attiva = he/she activates

Since la leva is singular and means it, the correct form is attiva.

This sentence follows the very common Italian word order:

Subject + Verb + Object

• La leva = subject
• attiva = verb
• il meccanismo = direct object

This is the same basic order as in English:

• The lever activates the mechanism.

Italian can sometimes change word order for emphasis or style, but this standard order is the most neutral and common.

In this sentence, the most natural reading is:

• La leva = the subject, the thing doing the action
• il meccanismo = the object, the thing receiving the action

You can tell this mainly from:

1. Word order
   Italian often puts the subject before the verb and the object after it.

2. Meaning of the verb structure
   attivare is a transitive verb, so it usually takes a direct object after it.

So the structure is:

• The lever activates the mechanism

Because attivare is a transitive verb. That means it can take a direct object directly, without a preposition.

So:

• attivare qualcosa = to activate something

Examples:

• attiva il motore = activates the engine
• attiva il sistema = activates the system
• attiva il meccanismo = activates the mechanism

You do not need a preposition like a or di here.

By itself, yes: attiva can be the feminine singular adjective meaning active.

For example:

• La macchina è attiva. = The machine is active.

But in La leva attiva il meccanismo, it is not an adjective. If it were an adjective, the sentence would not make sense in this structure, because you would still need a main verb somewhere.

So in this sentence, context and structure tell you that attiva must be the verb activates.

A simple pronunciation guide is:

la LEH-va at-TEE-va eel meh-kka-NEE-zmo

A few useful points:

• leva: stress on LE
• attiva: stress on TI
• il: pronounced like eel
• meccanismo: stress on NI

Also, in meccanismo, the cc before a is a hard k sound, so it sounds like mek-ka-.

Because meccanismo begins with a normal consonant sound, m, so the standard masculine singular article is il.

Use lo with masculine singular nouns beginning with certain special sounds, such as:

• z: lo zaino
• s
  • consonant: lo studente
• ps: lo psicologo
• gn: lo gnomo

But:

• il meccanismo
• il motore
• il manuale

So il meccanismo is exactly what you would expect.

Yes. Both the articles and the verb would change.

Singular:

• La leva attiva il meccanismo.
• The lever activates the mechanism.

Plural:

• Le leve attivano i meccanismi.
• The levers activate the mechanisms.

Changes:

• la → le
• leva → leve
• attiva → attivano
• il → i
• meccanismo → meccanismi

This shows how Italian marks number more visibly than English does.

Italian often allows the subject pronoun to be omitted:

• Attiva il meccanismo. = It activates the mechanism / He/she activates the mechanism, depending on context

But here the subject is not a pronoun like it. It is a full noun phrase:

• la leva = the lever

If you want to say exactly what performs the action, you include it. So La leva attiva il meccanismo is the clear, complete sentence.