Sen poprawia pamięć.

• Sen = the subject of the sentence, in the nominative singular
• poprawia = the verb, 3rd person singular present
• pamięć = the direct object, in the accusative singular

So structurally it is:

[Subject] + [Verb] + [Object]
Sen + poprawia + pamięć

Poprawia comes from the infinitive poprawiać, which is imperfective.

That is the natural choice here because the sentence expresses a general fact or habitual truth:

• Sen poprawia pamięć. = Sleep improves memory.

The perfective partner is poprawić. A perfective verb would not normally be used here to express a general truth in the present.

So:

• poprawiać → imperfective, used for ongoing/general/repeated situations
• poprawić → perfective, used for a completed improvement

It can technically match either in English, because Polish present tense often covers both:

• improves
• is improving

But in this sentence, the normal interpretation is a general statement:

Sleep improves memory.

It is not usually understood as a description of something happening right this second.

That is a very common question.

Many feminine nouns in Polish do change in the accusative, for example:

• kobieta → kobietę

But pamięć is a different type of feminine noun. It does not end in -a. Its accusative singular is the same as its nominative singular:

• nominative: pamięć
• accusative: pamięć

So in Sen poprawia pamięć, the object is indeed accusative, even though the form does not visibly change.

It is accusative singular here because it is the direct object of poprawia.

A useful thing to know is that for this noun:

• Nominative: pamięć
• Accusative: pamięć
• Genitive: pamięci

So the accusative happens to look identical to the nominative.

In this sentence, the main clue is word order and meaning.

Both nouns have forms that could look like nominative or accusative:

• sen can be nominative singular
• pamięć can also look the same in nominative and accusative singular

So the sentence is understood as:

• Sen = subject
• pamięć = object

because Polish usually defaults to reading the first noun as the subject when the forms do not clearly distinguish subject and object.

So:

• Sen poprawia pamięć = Sleep improves memory
• Pamięć poprawia sen would normally mean Memory improves sleep

Word order matters a lot here.

You can, but you should be careful.

Because sen and pamięć do not clearly show different endings here, changing the order may change who is understood as doing the action.

• Sen poprawia pamięć. = Sleep improves memory.
• Pamięć poprawia sen. = usually Memory improves sleep.

So this is not a good sentence for free word-order experimentation unless the context makes the meaning obvious.

Polish has no articles.

So Polish does not use separate words for:

• a
• an
• the

That means Sen poprawia pamięć can correspond to English without any article words:

• Sleep improves memory

Whether something is the, a, or just a general concept is understood from context.

Yes. Sen can mean:

• sleep
• dream

Context tells you which one is meant.

In Sen poprawia pamięć, the natural meaning is clearly sleep, not dream, because dream improves memory would be a very unusual interpretation.

Yes, there is a nuance.

• sen usually refers to sleep as a state or phenomenon
• spanie is more like sleeping, emphasizing the activity/process

So:

• Sen poprawia pamięć = a natural, concise general statement
• Spanie poprawia pamięć is also understandable, but it sounds more like sleeping improves memory

In many contexts both can work, but sen is very natural here.

A rough English-friendly guide:

• Sen ≈ sen
• poprawia ≈ po-PRA-vya
• pamięć ≈ PA-myench

A few important pronunciation notes:

• w in Polish sounds like English v
• ę in pamięć does not sound exactly like English en, but before ć it is often pronounced close to eń
• ć is a soft sound, somewhat like a very soft ch/tch

Stress:

• SEN
• po-PRA-wia
• PA-mięć

Polish normally stresses the second-to-last syllable, though in a two-syllable word like pamięć, that means the first syllable is stressed.

The dictionary forms are:

• sen → noun, sleep
• poprawiać → infinitive, to improve
• pamięć → noun, memory

So poprawia is just the conjugated form of poprawiać.

In standard Polish, the direct object often changes to the genitive after negation.

So:

• Sen poprawia pamięć. = Sleep improves memory.
• Sen nie poprawia pamięci. = Sleep does not improve memory.

Notice the change:

• pamięć → pamięci

This is a very important Polish pattern called the genitive after negation.