A veces confundo el singular con el plural cuando escribo deprisa.

Because Spanish often leaves out subject pronouns when the verb ending already shows who is doing the action.

Here, confundo and escribo both clearly mean I confuse and I write, so yo is not necessary.

• (Yo) confundo = I confuse / I mix up
• (Yo) escribo = I write

You could say Yo a veces confundo... if you wanted extra emphasis or contrast, but most of the time it sounds more natural without yo.

A veces means sometimes.

It is often placed at the beginning of the sentence, just like in English, but it can move around:

• A veces confundo el singular con el plural...
• Confundo a veces el singular con el plural...

The first version is the most neutral and common. Putting a veces first helps set the scene right away: this happens sometimes, not always.

Confundo is the first person singular present tense of the verb confundir = to confuse / to mix up.

So:

• confundo = I confuse / I mix up
• confuso = confused or confusing-looking in some contexts, but it is an adjective
• confundido = confused, usually as a past participle or adjective

In this sentence, you need a verb, because the speaker is describing an action:

• A veces confundo... = Sometimes I mix up...

If you said estoy confundido, that would mean I am confused, which is a different idea.

Here singular and plural are being used as nouns, not just as adjectives.

In English, we also do this:

• the singular
• the plural

Spanish does the same thing, and when these grammar terms are used as nouns, they normally take the article:

• el singular
• el plural

So the sentence is talking about grammatical categories: the singular and the plural.

Because confundir normally uses the pattern:

• confundir X con Y = to confuse X with Y

So:

• Confundo el singular con el plural = I confuse the singular with the plural

This is the standard construction in Spanish. It works very much like English confuse X with Y.

More examples:

• Confundo a Ana con su hermana. = I confuse Ana with her sister.
• Confunden la izquierda con la derecha. = They mix up left and right.

Because after cuando you normally need a conjugated verb, not a gerund by itself.

So Spanish says:

• cuando escribo = when I write
• cuando trabajo = when I work

Not:

• cuando escribiendo ❌

If you want to express while writing, Spanish could use something like:

• al escribir deprisa
• mientras escribo deprisa

But in your sentence, cuando escribo deprisa is the natural way to say when I write quickly or when I’m writing quickly, especially for a general repeated situation.

The present tense is used because the sentence describes a habitual or repeated action:

• A veces confundo... = Sometimes I mix up...
• cuando escribo deprisa = when I write quickly

Spanish, like English, often uses the present tense for habits and general truths.

It does not necessarily mean the person is doing it right now. It means this is something that happens from time to time.

Deprisa means quickly / in a hurry / fast.

In this sentence, escribo deprisa means I write quickly.

It is very common in Spain. You will also hear:

• rápido as an adverb in informal speech: escribo rápido
• rápidamente, which is more formal or more explicitly adverbial

All of these can work, but deprisa is very natural in Spain.

A rough comparison:

• deprisa = very common, natural, everyday
• rápido = also common in speech
• rápidamente = correct, but often sounds a bit more formal or deliberate

It can correspond to either one in English, depending on context.

Spanish present tense often covers both:

• when I write quickly
• when I’m writing quickly

In this sentence, the meaning is general and habitual, so when I write quickly is probably the most direct translation. But the idea of when I’m writing quickly is also built into the Spanish.

Yes, Spanish word order is flexible, and this sentence could be rearranged without changing the basic meaning.

For example:

• A veces confundo el singular con el plural cuando escribo deprisa.
• Cuando escribo deprisa, a veces confundo el singular con el plural.

Both are natural.

The difference is mostly one of emphasis:

• Starting with A veces highlights frequency
• Starting with Cuando escribo deprisa highlights the situation or condition

The original version is perfectly natural and balanced.

In these grammar expressions, yes:

• el singular
• el plural

That is because the words singular and plural are masculine when used this way as nouns referring to grammatical number.

You may also hear fuller versions such as:

• el número singular
• el número plural

Since número is masculine, that matches el as well.

A simple pronunciation guide:

• confundo ≈ kon-FOON-do
• deprisa ≈ deh-PREE-sa

A few useful notes:

• In confundo, the stress is on fun
• In deprisa, the stress is on pri
• The d in deprisa is softer than English d
• In Spain, z and c before e/i have the th sound of thin, but that does not affect these two words

Also:

• singular ≈ seen-goo-LAR
• plural ≈ ploo-RAL

Not in the same way here.

• Confundo el singular con el plural = I mix up the singular and the plural
• Me confundo = I get confused

So me confundo focuses more on myself becoming confused, while confundo X con Y focuses on mixing one thing up with another.

You could say:

• A veces me confundo cuando escribo deprisa. = Sometimes I get confused when I write quickly.

But that is less specific than the original sentence. The original clearly says what gets mixed up: the singular and the plural.

Yes. The whole sentence is natural in general Spanish, but deprisa is especially common and everyday in Spain.

A speaker from Latin America would still understand it perfectly, but depending on the country, they might be more likely to say:

• rápido
• rápidamente

So the sentence sounds fully correct everywhere, while also fitting well with Spain usage.