what is it?
Spanish makes two small but obligatory spelling changes to its coordinating conjunctions to avoid awkward sound collisions: y («and») becomes e before any word whose first sound is /i/, and o («or») becomes u before any word beginning with o- or ho-. Separately, the connectors por eso and entonces introduce a result or consequence, equivalent to «so» or «therefore» in English.
when to use it
y → e: use e whenever the following word begins with the vowel sound /i/ — whether spelled i- or hi- (where the h is silent and the i is a full vowel, e.g. historia, hijo).
Exception — hie-: keep y before words beginning with hie- (e.g. hielo, hierro). Here the hie- is a diphthong starting with the glide /j/, not a pure /i/ vowel, so no clash occurs.
o → u: use u whenever the following word begins with o- or ho- (e.g. once, ocho, hora).
por eso / entonces: use either connector to link a cause to its result. Por eso is slightly more emphatic («that is why»); entonces is more neutral («so, then»). Both can start a new sentence or follow a semicolon.
formation
The substitution is purely phonological — no other part of the sentence changes. The table below summarises the trigger and the resulting form.
| base form | trigger | use instead | example |
|---|---|---|---|
| y | next word starts with /i/ sound (i-, hi-) | e | padre e hijo |
| y | next word starts with hie- (glide /j/) | y (no change) | agua y hielo |
| o | next word starts with o- or ho- | u | diez u once |
For consequence connectors, the structure is simply: [cause clause] + por eso / entonces + [result clause]. A period or semicolon separates the two clauses; the connector is not preceded by a comma when it opens a new sentence.
examples in context
common pitfalls
Keeping y before an /i/ sound. Writing «Fernando y Ignacio» is incorrect. Whenever the next word starts with the vowel sound /i/ — whether spelled i- or a silent-h hi- — y must become e: «Fernando e Ignacio».
Applying e-substitution before hie-. Writing «agua e hielo» is incorrect. The hie- sequence is a diphthong beginning with the consonantal glide /j/, so no vowel clash occurs and y is kept: «agua y hielo».
Keeping o before o- or ho-. Writing «diez o once» is incorrect. Before any word beginning with o- or ho-, o must become u: «diez u once».
The trigger for both substitutions is sound, not spelling. Always ask what the first sound of the next word is, not just its first letter.
Three sentences, graded here. Nothing is saved and no account is needed.
En la gasolinera vendían gasolina ___ hierba seca para los caballos.
Fill in the blank with the correct connector (y or e).