Why is it that "appreciate" is pronounced as though it were "appreshiate?"
In general, English words spelled with "ci", "ti" or "si" before a vowel letter are often pronounced with a "sh" sound /ʃ/ rather than a "s" sound /s/. This phenomenon is called "palatalization," and it is described in the answers to the following questions:
- How to pronounce to differ spatial from special?
- What rules of English allow the first t in “patient” to make an sh sound?
- Is there a simple guide for 's' vs 'sh' pronunciation in words?
The answers I linked to above mostly discuss words like social /ˈsoʊʃəl/ and initial /ɪˈnɪʃəl/ where there is no distinct "i" sound after the /ʃ/. However, there are also some words where "ti" or "ci" before a vowel letter is pronounced as /ʃi/, the combination of the "sh" consonant and a short unstressed "ee" sound (in some older British dialects, the sound used in words like this was more like "ih"). This includes words like associate (v.) /əˈsoʊʃieɪt/, appreciate /əˈpriːʃieɪt/, and initiate (v) /ɪˈnɪʃieɪt/.
It seems that this pronunciation is used for words ending in -iate, as well as further derivatives of these such as words ending in -iation. More generally, a pronunciation with /ʃi/ often seems to be possible when the following vowel letter represents an "unreduced" vowel sound like /eɪ/, /oʊ/ (ratio), /ɒ~ɑ/ (preciosity), /ɛ/ (conscientious), or /æ/ (partiality).
For some of these words, a pronunciation with /si/ is also possible; you should check a dictionary to see if that is the case for any particular word. For example, the Oxford Advanced Learner's Dictionary lists an alternate pronunciation with /si/ for associate, but not for appreciate or initiate.
Another reason to check the dictionary: some words with similar spellings are never pronounced with /ʃ/, such as pronunciation and calcium, for which the Oxford Advanced Learner's Dictionary lists only the pronunciation with /si/.
By the way, this kind of palatalization can also affect many other words such as those spelled with "ce" (ocean); it generally occurs in words spelled with t, c, ss, s, or z or before i or e followed by another vowel letter (a non-exhaustive list of possible environments for palatalization: "ia", "ie", "io", "iu", "ea"), resulting in pronunciations with fricatives like /ʃ/ or /ʒ/.
When "t" comes after the letter "s", it doesn't palatalize to /ʃ/ but to /tʃ/ (as in "Christianity" /krɪstʃiˈænɪti/). This rule also applies to words ending in -stion, like "question" /kwɛstʃən/.
Another, slightly different kind of palatalization occurs in words spelled with ss, s, z, t, or d before unstressed "long u" (often in the ending "-ure"), resulting in pronunciations with fricatives like /ʃ/ or /ʒ/ or affricates like /tʃ/ or /dʒ/.
Take a look at this video. It seems that you can also pronunce it as in "see".