Alternations
A number of alternations exist in Spanish that reflect diachronic changes in the language and arguably reflect morphophonological processes rather than strictly phonological ones. For instance, a number of words alternate between /k/ and /θ/ or /ɡ/ and /x/, with the latter in each pair appearing before a front vowel:
| word | gloss | word | gloss | ||
|---|---|---|---|---|---|
| opaco | /oˈpako/ | 'opaque' | opacidad | /opaθiˈdad/ | 'opacity' |
| sueco | /ˈsweko/ | 'Swedish' | Suecia | /ˈsweθja/ | 'Sweden' |
| belga | /ˈbelɡa/ | 'Belgian' | Bélgica | /ˈbelxika/ | 'Belgium' |
| análogo | /aˈnaloɡo/ | 'analogous' | analogía | /analoˈxia/ | 'analogy' |
Note that the conjugation of most verbs with a stem ending in /k/ or /g/ does not show this alternation; these segments do not turn into /θ/ or /x/ before a front vowel:
| word | gloss | word | gloss | ||
|---|---|---|---|---|---|
| seco | /ˈseko/ | 'I dry' | seque | /ˈseke/ | '(that) I/he/she dry (subjunctive)' |
| castigo | /kasˈtiɡo/ | 'I punish' | castigue | /kasˈtiɡe/ | '(that) I/he/she punish (subjunctive)' |
There are also alternations between unstressed /e/ and /o/ and stressed /je/ and /we/ respectively:
| word | gloss | word | gloss | ||
|---|---|---|---|---|---|
| heló | /eˈlo/ | 'it froze' | hiela | /ˈjela/ | 'it freezes' |
| tostó | /tosˈto/ | 'he toasted' | tuesto | /ˈtwesto/ | 'I toast' |
Likewise, in a very small number of words, alternations occur between the palatal sonorants /ʎ ɲ/ and their corresponding alveolar sonorants /l n/ (doncella/doncel 'maiden'/'youth', desdeñar/desdén 'to scorn'/'scorn'). This alternation does not appear in verbal or nominal inflection (that is, the plural of doncel is donceles, not *doncelles). This is the result of geminated /ll/ and /nn/ of Vulgar Latin (the origin of /ʎ/ and /ɲ/, respectively) degeminating and then depalatalizing in coda position. Words without any palatal-alveolar allomorphy are the result of historical borrowings.
Other alternations include /ks/ ~ /x/ (anexo vs anejo), /kt/ ~ /tʃ/ (nocturno vs noche). Here the forms with /ks/ and /kt/ are historical borrowings and the forms with /x/ and /tʃ/ forms are inherited from Vulgar Latin.
There are also pairs that show antepenultimate stress in nouns and adjectives but penultimate stress in synonymous verbs (vómito 'vomit' vs. vomito 'I vomit').
Read more about this topic: Spanish Phonology