Why does the first one work, but the second doesn't?

doesnt_work

pyg = 'ay'

original = raw_input('Enter a word:')

if len(original) > 0 and original.isalpha():
    word = original.lower()
    first = word[0]
    if first == "a" or "e" or "i" or "o" or "u":
      print "vowel"
    else:
    	print "consonant"
else:
    print 'empty'

works

pyg = 'ay'

original = raw_input('Enter a word:')

if len(original) > 0 and original.isalpha():
    word = original.lower()
    first = word[0]
    if first == "a" or first == "e" or first == "i" or first == "o" or first == "u":
      print "vowel"
    else:
    	print "consonant"
else:
    print 'empty'