title_body: Four vowels, with no /i/ sound. Is it possible? My vowel phonemic inventory would be just /a/, /e/, /o/ and /u/ with no /i/ sound. Is this possible or not?
upvoted_answer: This would be very unstable in a human language. For an example of what happens when this vowel is missing, let's look at English's Great Vowel Shift. One of the first things to change was /i:/ becoming /aj/, leaving it without /i/. Within less than a hundred years, /e:/ had migrated to take its place. 
  
  In your specific case, I would expect /e/ -> /i/, /a/ -> /e/, and /o/ -> /ɒ/ in fairly short order.
  
  This is because vowels like to spread out on the vowel chart and become more distinct to improve understanding. Because of the limitations of your mouth making it difficult to have highly fronted low vowels, the general rule is that you will have more high vowels than mid or low vowels. Your vowel system violates this universal (with more mid vowels than high vowels).