Unstressed vowels in English often delete. The deleted vowel is always a schwa and may thus be termed schwa deletion. In words which end with the suffix -ly, schwa deletion often occurs.
Schwa deletion occurs in the following words:
basically
chronically
dynamically
historically
idealistically
musically
philosophically
physically
pyschologically
realistically
However, schwa deletion usually does not occur in these words:
accidentally
communally
finally
formally
internally
materially
mentally
normally
terminally
totally
Though the two sets of words both end with -ally, they are different. In the set with vowel deletion, the root ends with a [k]. This is a velar plosive and is classified as [-coronal]. However, in the second set, the root ends with [l], [n] and [t]. These sounds are all [+coronal]. With coronal sounds, schwa deletion usually does not occur.
In words such as basically, dynamically and physically, schwa deletion creates a consonant cluster which is very common in the English syllable onset. It occurs in words such as clay, clean and cloud. However, no consonant clusters occur with adjacent coronal consonants.
Schwa deletion is a common process in English. However, it does not occur in all possible environments. Between coronal consonants, it is far less common than in other consonants.