I am just learning Spanish. For the most part, I find that pronunciation is very consistent. However, I am having a little difficulty with the letter "C." Most of the time it is pronounced like "K" in English, but there are exceptions. In the word "Discipulos" it appears to be silent; in "Cierto" it is pronounced like "S" in English. Are there rules for determining when C is silent, and when it is pronounced like "S" or do I just need to memorize these exceptions?
C is never silent.
'c' has three sounds.
When combined with 'h' it creates the digraph 'ch' with the same sound as english 'chair' ('choza').
When followed by 'a', 'o' or 'u' or by another consonant it has the 'k' sound ('casa', 'cobre', 'ósculo', 'actor').
When followed by 'e' or 'i' it has the 'z' sound ('cereza', 'ciruela').
Your problem arises with this third sound. Spanish is divided in two big areas that we can call "standard" and "seseante" (Spanish word for 's-using'). In "seseante" zones (you are learning in one of them, and they are majority through Latin America) the 'z' sound has disappeared and both 'z' and 'ce'-'ci' are pronounced as 's'. So with "discípulos": on a "seseante" zone you have an 's' followed by an 's' sound, and since there is no long 's' in Spanish you end up pronouncing just one 's'.
Zone Discípulos Cereza Casa Choza Acción Standard Dis-ZI-pu-los ze-RE-za CA-sa CHO-za ak-ZION Seseante Di-SI-pu-los se-RE-sa CA-sa CHO-sa ak-SION
I would add something to @Envite answer (I can't comment):
In spanish the sound it's more important than the way of writing (always respecting the orthografy). This means that if a word changes you have to update the way you write it.
Also, the 'z' before 'i' and 'e' it's almost forbbiden, it turns into 'c', except for very few words for ethimological reasons ("enzima", "zinc","azimut","nazi","zigzag") and in "zeta" (because is it's own name).
This is important in making plurals:
- "procaz" --> "procaces"
- "audaz" --> "audaces"
- "pez" --> "peces"
- "maíz" --> "maíces"
- "vez" --> "veces"
- "nuez" --> "nueces"
- "arroz" --> "arroces"
- "luz" --> "luces"
- "tenaz" --> "tenaces"
- "matiz" --> "matices"
- And a lot more.
And with the "conjugación" of the verbs:
- "cazar" -> "cace" (1ª s.), "cacemos" (1ª p.)…
- "cocer" -> "cuezo" (1ª s.), "cueza" (another tense), …
- "zurcir" -> "zurzo"…
- "sacar" -> "saque" (1ª s.) and "saquemos" (1ª p.).
You are right in American Spanish the sequences -sci- and -sce- are pronunced always /si/ and /se/ (in European Spanish the most frequent pronunciations are /-sθi-/ and /-sθe-/).
One might expect that the equalization in American Spanish of /s/ and /θ/ would lead to forms such as */-s:e-/ or */-s:i-/, but this is not the case, since Spanish language lacks tense or geminate consonants as Italian does. In American Spanish /-sce-/ and /-sci-/ are pronounced always with a plain consonant:
ascensor [asen'soɾ] // consciente [kon'sjente]