Knowing whether to spell a word -ía or -ia

Question

If I hear the word pronounced, I can tell whether it's -ía or -ia based on whether the "i" has its own syllable or not. Likewise, I can look it up in a dictionary. But apart from that, how can I tell if I should use the tilde or not?

An example of a word with the ending of -ía is sangría, which according to Wiktionary has an etymology of "From sangre (“blood”) +‎ -ía".

An example of a word with the ending of -ia is altisonancia, which according to Wiktionary has an etymology of "altisonante +‎ -ia".

Words borrowed from Latin and then Ancient Greek don't seem to be any more consistent. One word with -ía is policía, which is "From Latin politīa, from Ancient Greek πολιτεία (politeía)." One word with -ia is historia which is "Borrowed from Latin historia, from Ancient Greek ἱστορία (historía)."

One piece of useful information I found was that -ería is a common suffix, while there doesn't seem to be a suffix of "-eria". (Are there any words ending with eria?)

Answer 1

As can be seen from your examples, it is often arbitrary, and many times the presence or absence of an accent on the /i/ already happened in a previous etimological step (Latin historia vs politīa). So in many cases, one just has to learn the specific cases by heart, or dig up their etymology.

As you said, there are some suffixes that make this task easier. The following is a non-exhaustive list:

Without accent

• Nouns ending in -ncia coming from adjectives ending in -nte: redundancia, resistencia. Exception: mercancía. Note also: alcancía does not come from an adjective.

• Adjectives ending in -ario, -aria: becaria, monetaria

• Present tense of most verbs in -iar whose infinitive has more than two syllables: alivia, escancia. But not all: avería.

• Most words ending in -eria without this being a suffix or verb tense as explained below seem to not take an accent: materia, bacteria

• Most countries: Alemania, Finlandia. Exception: Turquía.

• Suffix -cracia, meaning "power, government": democracia, aristocracia.

• Suffix -algia, meaning "pain": nostalgia, mialgia.

With accent

• Verb tenses: first and third person singular of condicional of all verbs (cantaría, bebería) and pretérito imperfecto of verbs in -er, -ir (comía, vivía).

• Present tense of most verbs in -iar whose infinitive has one or two syllables: fía, amplía. But not all: cambia.

• Suffix -ería for shops, sets, or for making nouns out of adjectives: carnicería, palabrería, pedantería.

• Suffixes -logía for sciences (geología, antropología) and -sofía (filosofía).

• Suffix -nomía meaning "set of laws/rules": autonomía, astronomía. Exception: antinomia.

• Suffix -fonía meaning "sound": afonía, cacofonía.

• Suffix -arquía, meaning "power, government": monarquía, jerarquía.