The main difference between vowels and consonants is that consonants are sounds that are made by constricting airflow through the mouth. When a consonant is pronounced, the teeth, lips or tongue pinch together, while vowels are pronounced through an open mouth.
Consonants and vowels are the two different building blocks of speech. The English vowels are represented by the letters a, e, i, o and u, whereas the consonants make up the rest of the letters in the alphabet. Consonant sounds are made in many different ways, all of which involve blocking airflow through the mouth by moving the tongue or lips. Vowel sounds are made with an open mouth and are characterized by their length, the position of the open mouth from beginning to end and whether airflow is also occurring through the nose during pronunciation.
In human languages, vowels typically occur in the middle of syllables, with a consonant before or after. Consonants occur on the margins of syllables, often indicating breaks from one syllable to the next. Some English words consist of a single syllable made up of a vowel that is not followed by a consonant, such as "a" or "I," but this is rare.