kasikoi inu ga kagi wo mitukemasita.

It is read:

かしこい いぬ が かぎ を みつけました。

A full reading breakdown:

• 賢い = かしこい
• 犬 = いぬ
• が = が
• 鍵 = かぎ
• を = を
  In modern Japanese, を is pronounced お.
• 見つけました = みつけました

In Japanese, adjectives usually come before the noun they describe, just like in English.

So:

• 賢い犬 = smart dog / clever dog

Here, 賢い directly modifies 犬.

Because 賢い is an い-adjective.

Japanese has two main adjective types:

• い-adjectives: end in い
  Example: 賢い, 高い, 新しい
• な-adjectives: need な before a noun
  Example: 静かな犬 = a quiet dog

Since 賢い is an い-adjective, it attaches directly to the noun:

• 賢い犬

Not:

• 賢な犬

が marks the subject of the sentence.

Here:

• 賢い犬が = the smart dog is the one doing the action

So が tells you that the smart dog is the thing that found something.

A simple structure is:

• [subject] が [object] を [verb]

In this sentence:

• 賢い犬 = subject
• 鍵 = object
• 見つけました = verb

This is a very common question.

Both が and は can sometimes appear in similar places, but they are not the same.

Here, が marks the grammatical subject:

• 賢い犬が鍵を見つけました。

If you used は instead:

• 賢い犬は鍵を見つけました。

That would sound more like:

• As for the smart dog, it found the key
• or it may suggest contrast, depending on context

Very roughly:

• が = focuses on who did it
• は = introduces or highlights the topic

In a simple standalone sentence like this, が is very natural.

を marks the direct object of the verb.

Here:

• 鍵を = the key is the thing being found

So:

• 犬が = the dog does the action
• 鍵を = the key receives the action
• 見つけました = found

Even though を is written with the kana を, it is pronounced お.

見つけました is the polite past form of the verb 見つける, which means to find.

Breakdown:

• dictionary form: 見つける
• polite non-past: 見つけます
• polite past: 見つけました

So 見つけました means:

• found
• or more literally, did find in polite style

This makes the whole sentence polite and natural in standard speech.

Because Japanese normally uses SOV word order:

• Subject – Object – Verb

English is usually SVO:

• The smart dog found the key.

Japanese:

• 賢い犬が 鍵を 見つけました。
• literally: Smart dog + subject marker + key + object marker + found

The verb usually comes at the end of the sentence in Japanese.

Japanese word order is more flexible than English because particles show each word’s role.

So this sentence could also appear as:

• 鍵を賢い犬が見つけました。

This still means roughly the same thing, because:

• が still marks the subject
• を still marks the object

However, changing the order can change the focus or emphasis. The original version is the most straightforward and neutral.

Japanese usually does not have articles like a, an, or the.

So 鍵 could mean:

• a key
• the key
• keys in some contexts

The exact meaning depends on context.

In a simple sentence by itself, English translators have to choose what sounds best, but Japanese often leaves that unspecified.

Usually, you don’t know from the noun alone.

Japanese nouns often do not change for singular vs. plural:

• 犬 can mean dog or dogs
• 鍵 can mean key or keys

Context usually tells you which is meant.

In this sentence, most people would naturally read it as singular:

• The smart dog found the key or
• A smart dog found a key

But the Japanese itself does not force singular as strongly as English does.

Here is a quick kanji breakdown:

• 賢 in 賢い = wise, clever
• 犬 = dog
• 鍵 = key
• 見 in 見つけました = see
• つける in 見つける helps form the verb to find / to discover

A useful note:

• 見つける is a whole verb meaning to find
• It is better to learn it as one vocabulary item, not just as separate pieces

The casual past version would be:

賢い犬が鍵を見つけた。

The difference is:

• 見つけました = polite past
• 見つけた = casual past

So the meaning stays the same, but the level of politeness changes.

The spaces are probably just for learners.

Normal Japanese is usually written without spaces:

賢い犬が鍵を見つけました。

Japanese readers rely on:

• kanji
• kana
• particles
• grammar patterns

to see where words begin and end. Educational materials often add spaces to make sentences easier to read at first.