Coordinación: y, o, pero, sino

The Spanish coordinating conjunctions — y, o, pero, sino — are among the first words a learner meets, but they have grammatical wrinkles that take longer to master than their straightforward meanings suggest. Y changes shape to e before certain vowels. O changes to u. Pero and sino both translate to English "but," but they cover non-overlapping territory and are not interchangeable. Layered on top of these are two clause-level variants — sino que and the literary mas — that round out the inventory.

This page covers all four conjunctions, their phonological alternations, the pero / sino distinction (a frequent source of error), and the brief note on mas that explains why you see it in poetry but never in conversation.

Y — "and"

The default coordinator: joins phrases, clauses, and sentences.

Note: Spanish does not use the Oxford comma. The list pan, leche y huevos puts no comma before y.

Y becomes e before i- or hi-

When the next word starts with the vowel sound /i/ — that is, with the letter i- or with hi- (where the h is silent) — Spanish replaces y with e to avoid the awkward /i i/ collision.

The hie- exception

When the next word starts with hie- — hielo, hierro, hierba, hiedra — the h is silent but the ie- is pronounced as a diphthong (/je/, like English yeah), not as a plain vowel. The collision y / je doesn't happen, so the conjunction stays as y.

The rule is purely phonological: it follows what the next word sounds like, not how it's spelled. Hielo starts with /je/, so y hielo is fine. Hijos starts with /i/, so it triggers the change to e hijos.

Y with questions

When y opens a question to mean "and what about…?", it still alternates normally with e:

O — "or"

The default disjunction: offers alternatives.

O becomes u before o- or ho-

By the same logic as y / e, when the next word starts with the vowel sound /o/ — that is, with o- or ho- (silent h) — Spanish replaces o with u.

There is no hue- exception to learn here equivalent to hie-; the /we/ sound (as in hueso) likewise doesn't collide with /o/, so o hueso would stay as o. But because the /o/ + /o/ collision is what matters, the rule kicks in cleanly: u before any word starting with /o/.

O used between numbers

There used to be an orthographic convention of writing ó between numbers (3 ó 4) to disambiguate from a zero. The current RAE norm (since 2010) abolishes this accent — write 3 o 4, never 3 ó 4. The accented form is now considered an error.

Pero — "but" (contrast)

Pero introduces a contrast between two statements that are both true. The second clause qualifies, modifies, or adds friction to the first, but does not negate it.

The key feature: pero expects both clauses to be true. Es caro pero merece la pena asserts both that it's expensive and that it's worth it. The contrast is in the implication ("expensive things often aren't worth it"), not in the truth values.

Sino — "but rather" (correction after negation)

Sino introduces a correction: the first clause is negated, and sino offers the right answer to replace what was negated.

The semantic structure: no X, sino Y asserts that Y is the right value where X was the wrong one. The two are mutually exclusive: you can't have no es caro sino barato and es caro pero barato mean the same thing, because the first denies caro while the second affirms it.

The pero vs sino test

Whenever you're about to write but after a negative, run this test: would the sentence make sense if you replaced but with "but rather" in English? If yes, use sino. If you would say "but anyway" or "but on the other hand," use pero.

The compact rule: sino replaces the negated element; pero adds to it.

Sino que — clause-introducing sino

When the correction introduced by sino is a full clause (with its own verb), Spanish requires the linker sino que.

The que is obligatory when the sino-clause has its own conjugated verb. Forgetting it (❌no me llamó, sino vino) is one of the most frequent intermediate-level errors. The rule is mechanical: phrase → sino; clause → sino que.

The construction no solo X sino (que) también Y — "not only X but also Y" — is covered in detail on the correlatives page.

Mas — literary "but"

Mas (no accent) is the literary equivalent of pero. You will encounter it in poetry, in literary prose, in song lyrics, and in some formal writing. In everyday spoken Spanish it is archaic / literary — a Spaniard would never use mas in conversation.

Notice the accent on más (more) versus the no-accent mas (but). The first is everyday, the second is the literary conjunction. Mixing them up is a common written error even among native speakers — write mas (no accent) only when you mean "but" in a literary register.

Ni — "nor"

Ni coordinates negative elements. It is the negation of y, with parallel grammar.

The single-ni pattern (no X ni Y) is the everyday one. The correlative pattern (ni X ni Y) is more emphatic and is covered on the correlatives page. Ni also doubles as the emphatic-negation particle ("not even") covered on the fronting-and-focus page.

Agreement with coordinated subjects

When y joins two subjects, the verb is plural:

Note the person agreement in the second example: mi padre y yo takes first-person plural vamos. The rule of thumb: first person trumps second; second trumps third. Tú y yo → vamos / hablamos. Tú y él → vais / habláis.

When o joins two subjects, the verb is typically singular if the alternatives are exclusive:

But plural is also possible if the alternatives can both happen:

In practice, Spanish allows some flexibility; both podrá and podrán are acceptable, with the singular slightly more careful and the plural more common in everyday speech.

A note on commas

• Before y, o in a list: no comma (pan, leche y huevos).
• Before pero: comma is standard (es caro, pero merece la pena).
• Before sino: comma is standard when there's a pause; in short phrases the comma can be omitted (no es caro sino barato, or no es caro, sino barato).
• Before sino que: comma is standard.

These punctuation conventions are not strict, but they reflect what careful peninsular writers do.

Common Mistakes

Key takeaways

• Y → e before words starting with /i/ (i-, hi-). Exception: hie- stays as y (agua y hielo).
• O → u before words starting with /o/ (o-, ho-). The old ó between numbers is no longer used — write 3 o 4.
• Pero adds a contrasting but compatible point. Sino corrects after negation, replacing the wrong value with the right one.
• When the sino correction is a full clause with its own verb, you need sino que.
• Mas (no accent) is the literary "but" — keep it in poetry, not in conversation.
• Ni coordinates negatives; the correlative ni X ni Y form is more emphatic than bare no X ni Y.