No quiero ese; prefiero el segundo.

Ese means that one and refers to a specific masculine noun that is understood from context.

Eso is neuter and is used for that, that thing, or that idea, usually when no specific noun is being named.

So in No quiero ese, the speaker is really saying something like:

• No quiero ese libro. = I don’t want that book.
• No quiero ese. = I don’t want that one.

Because the hidden noun is masculine singular, ese is the correct form.

Here, ese is a demonstrative pronoun meaning that one.

The noun is omitted because both speakers already know what they are talking about. Spanish does this very often.

For example:

• No quiero ese coche. = I don’t want that car.
• No quiero ese. = I don’t want that one.

So ese replaces the noun instead of describing it.

Because Spanish often leaves out a noun when it is obvious from the situation.

This is called ellipsis. English does it too:

• I don’t want that one; I prefer the second.

Spanish works the same way here:

• ese = that one
• el segundo = the second one

A full version might be:

• No quiero ese libro; prefiero el segundo libro.

But that sounds repetitive if the noun is already clear.

Because segundo is being used as a noun-like expression: the second one.

When ordinal numbers are used this way in Spanish, they usually take the definite article:

• el primero = the first one
• el segundo = the second one
• el tercero = the third one

If you include the noun, then segundo works as an adjective:

• prefiero el segundo libro = I prefer the second book

Without the noun, el is needed:

• prefiero el segundo = I prefer the second one

Because Spanish usually leaves out subject pronouns when the verb ending already makes the subject clear.

• quiero = I want
• prefiero = I prefer

So No quiero ese; prefiero el segundo already clearly means I don’t want that one; I prefer the second one.

You could add yo for emphasis:

• Yo no quiero ese; prefiero el segundo.

But in a neutral sentence, leaving yo out is more natural.

This is the normal Spanish order:

• No
  • verb + object

So:

• No quiero ese = I do not want that one

Spanish puts no directly before the conjugated verb:

• No quiero
• No prefiero would mean I do not prefer

You would not normally say Quiero no ese for this meaning.

Both can mean that, but they usually refer to different distances.

In standard Spanish:

• este = this, near the speaker
• ese = that, near the listener or not especially far
• aquel = that over there, farther away from both

So ese in this sentence suggests that one rather than that one over there.

For example:

• No quiero ese; prefiero el segundo. = I don’t want that one.
• No quiero aquel; prefiero el segundo. = I don’t want that one over there.

In real life, people do not always follow the distance distinction perfectly, but this is the basic idea.

Modern standard Spanish normally writes demonstratives like este, ese, aquel without accent marks, even when they are pronouns.

So:

• Quiero ese.
• Prefiero este.

Older rules often allowed or recommended accents in pronoun use, such as ése, but that is no longer the general standard.

So ese without an accent is the normal modern spelling.

Both are present tense, first person singular:

• quiero = I want
• prefiero = I prefer

They come from:

• querer
• preferir

Both are irregular in the present tense:

• querer: quiero
• preferir: prefiero

In this sentence, they describe a present choice or preference.

The semicolon links two closely related statements:

• No quiero ese
• prefiero el segundo

It shows a stronger pause than a comma, but the ideas are still tightly connected.

You could also see:

• No quiero ese. Prefiero el segundo.
• No quiero ese, prefiero el segundo.
• No quiero ese; prefiero el segundo.

The semicolon is a neat, correct way to connect the two contrasting parts.

Yes, in everyday writing and speech, many people would say or write it that way.

However, the semicolon is more careful punctuation because the sentence really contains two complete clauses:

• No quiero ese
• prefiero el segundo

So the version with ; is especially clear and polished.

Usually yes, but the exact English translation depends on how it is being used.

Here, el segundo means the second one.

In other contexts:

• el segundo libro = the second book
• un segundo = one second

So segundo can be:

• an ordinal number: second
• a unit of time: second

In this sentence, it is clearly the ordinal number.

Yes, it sounds completely natural.

A speaker in Spain could easily say this when choosing between objects, options, menu items, clothes, tickets, and so on.

For example:

• choosing two shirts: No quiero ese; prefiero el segundo.
• looking at two apartments: No quiero ese; prefiero el segundo.

It is short, clear, and very normal Spanish.