always & never 均為頻率副詞

always & never 均為頻率副詞 (adverbs of frequency)，
我們用百分比來細分它們的差異：

always—100% all of the time

usually—80% most of the time

often—50% much of the time

sometimes—30% some of the time

seldom—almost never

never—not at any time