I’d been speaking Spanish for a couple of decades (well, maybe more) and teaching Spanish for a couple of years when it finally struck me, after red-inking yet another student paper with an abominable construction of the Paco’s libro ilk, that Spanish doesn’t use apostrophes at all.The apostrophe-free nature of Spanish is possible partly because we reverse the word order of possessives, saying el libro de Paco — no apostrophe required. But it’s mostly because Spanish doesn’t have contractions. (There are two exceptions: al “to the”, from a + el, and del “from the”, from de + el, but these were grandfathered in hundreds of years ago.) Contractions mean dropping a sound, an idea that is anathema in Spanish. All sounds are fully enunciated, even double vowels as in leer “to read” or cooperar. Dialectal variations that involve dropping sounds (like final –s in Andalucian and Caribbean Spanish) tend to be looked down on. This full pronunciation helps to give Spanish its characteristic staccato rhythm.
For good measure, Spanish short-circuits situations that might tempt speakers into the sin of contracting: specifically, cases where identical sounds come into contact at a word boundary. So the word o “or” changes to u before a word beginning with o, as in siete u ocho “7 or 8” (compare to seis o siete “6 or 7”). Likewise, y “and” becomes e before a word beginning with i, as in bonita e inteligente “pretty and smart” (compare to bonita y alta “pretty and tall”). A different strategy applies to the word la “the” when it precedes a feminine word beginning with a. Here, the Spanish solution is to substitute the masculine form el, as in el agua “the water.”
The three cases of u for o, e for y, and el for la are akin to the English swap of an for a before a vowel, as in an umbrella (compare to a raincoat): again, a pro-active change to keep the two words from running together.
Of course, the lack of an apostrophe means that Spanish teachers don’t have to wade through the tedium of teaching its proper usage, as must English teachers. We’re thus spared the agonies of brook’s versus brooks’ versus Mr. Brooks’s. ¡Lucky us!
Update from 2023: Since writing this post I’ve seen apostrophes used to represent colloquial abbreviations such as pa’ for para. This is completely in line with the use of the apostrophe to denote deleted sounds, as in contractions.