Distinguimos un defecto grave de un defecto muy grave.

In Spanish, subject pronouns are often omitted because the verb ending already shows who the subject is.

Distinguimos tells you the subject is we. So:

• Distinguimos = we distinguish
• Nosotros distinguimos = we distinguish, but with extra emphasis

You would usually add nosotros only if you want contrast or emphasis, for example:

• Nosotros distinguimos un defecto grave de un defecto muy grave, pero ellos no.

So in your sentence, leaving out nosotros is completely normal.

Here, distinguimos means we distinguish, we tell apart, or we differentiate.

The verb is distinguir.

A useful thing to know is that distinguimos can be either:

• present tense: we distinguish
• preterite: we distinguished

So this form is ambiguous by itself. In your sentence, it is most naturally understood as the present tense, especially if it is stating a general rule, definition, or procedure.

Because Spanish commonly uses the pattern:

distinguir A de B = to distinguish A from B

So:

• Distinguimos un defecto grave de un defecto muy grave
• literally: We distinguish a serious defect from a very serious defect

This is a very standard structure in Spanish.

English learners sometimes expect entre because English often uses between, but with distinguir, de is very common and natural.

Yes, you can hear structures with entre ... y ..., especially in some contexts, but distinguir X de Y is the classic and very standard pattern.

So:

• Distinguimos un defecto grave de un defecto muy grave = very natural
• Distinguimos entre un defecto grave y un defecto muy grave = also understandable, but the first version is more directly tied to the verb distinguir

For a learner, distinguir X de Y is the safest pattern to remember.

Spanish often repeats the noun for clarity, especially in formal, technical, or precise language.

So this sentence says:

• un defecto grave
• un defecto muy grave

Repeating defecto makes the contrast very explicit.

You could shorten it in some contexts:

• Distinguimos un defecto grave de uno muy grave.

That is also correct, and uno stands for un defecto. But the full repetition sounds more formal and precise, which fits well if this sentence comes from regulations, classification systems, or technical writing.

Not exactly. In this sentence, grave means serious or severe, not the English adjective grave in its more literary sense.

So:

• un defecto grave = a serious defect
• un defecto muy grave = a very serious defect

This is a very common Spanish use of grave.

Also, pronunciation is different from English. In Spanish, grave is pronounced roughly GRAH-beh, with two clear syllables.

Both are possible, but they are not always used in exactly the same way.

• muy grave = very serious
• gravísimo = extremely serious / very serious, with a stronger or more emphatic tone

In formal classifications, Spanish often prefers clear, transparent combinations like:

• leve
• grave
• muy grave

This is especially common in legal, administrative, educational, and technical language in Spain.

So muy grave sounds systematic and fits well in a scale of categories.

Because in Spanish, adjectives often come after the noun.

So:

• defecto grave = serious defect

This is the normal position for a descriptive adjective in Spanish.

If an adjective goes before the noun, it often adds a more subjective, literary, or emphatic nuance. But with classification-type language like this, the usual order is:

• noun + adjective

So defecto grave and defecto muy grave are exactly what you would expect.

Un is used because the sentence is talking about categories or types, not about two specific previously identified defects.

So the idea is something like:

• a serious defect
• a very serious defect

If you used el, it would sound like you were talking about a specific known defect:

• el defecto grave
• el defecto muy grave

That would be a different meaning. In your sentence, un is the natural choice because it refers to examples or classes within a classification.

Yes, it sounds fairly formal and technical.

The combination of:

• distinguir ... de ...
• repeated noun phrases
• categories like grave and muy grave

makes it sound like something from regulations, inspections, evaluation criteria, safety rules, or administrative documents.

In everyday conversation, a speaker might choose a simpler phrasing, but this sentence is perfectly natural in formal Spanish, especially in Spain.