When two vowels combine to make one sound, it is called a digraph. Long /e/ digraphs can be tricky. They can be written as ee as in seem, ea as in dream, or ie as in field. It can be challenging for children to recognize and spell digraphs because they must recognize the two letters together, rather than recognize a one-sound, one-letter correspondence. There are also times when the ea digraph does not make a long /e/ vowel sound, as in feather. 

Note: Vowel digraphs are often open vowels, as in bee and flea.