Besides weakening a vowel by making it more central, English frequently leaves out vowels or syllables altogether. This only happens to unstressed vowels and syllables. In the next section, Function Word Reductions, you start to learn how sentence stress leads to reductions and deletions, so this is not just at a word level.
Let’s look at a common word, “family.” If you put equal stress on every syllable and say it carefully, it will sound like:
fam ih lee [fæm ɪ li]
but that is not normal stress. The word has its stress on the first syllable, so it would normally be [ə].
FAM uh lee [fæm ə li]
Even if you put the stress equally on each syllable, it is unusual to use the [ɪ] sound and it is more usual to reduce it to [ə].
However, when being used in normal speech, the [ɪ] is usually left out entirely and people say:
FAM lee [fæm li]
That can make it confusing to know what word you are hearing. There are many English words that follow this pattern. Not all of them have an intermediate form because the reduced vowel is deleted. The progression is (usually):
V -> ə -> ∅
The vowel is reduced to schwa and then deleted. Here is a list of words where that happens.