 Diphthongs are vowels that undergo considerable change of quality during pronunciation. Let us illustrate the articulation of a diphthong. Here is the diphthong Au. Au. Au. Its starting point is A and then we gradually glide into OO. So diphthongs consist of an onset, that is the first element of a diphthong, and an offset, the final element. Both onset and offset are linked by a glide. Diphthongs can be classified in several ways. The most popular one uses the cardinal vowel chart and defines diphthongs on the basis of the direction of their glides as up gliding or closing, where the onset is lower than the offset, as down gliding or opening, where the onset is higher than the offset, and as in gliding or centering, where the offset is a central vowel. Here are some examples. Au can be classified as an up gliding diphthong. Ea is down gliding and air is in gliding. Additionally, we can specify diphthongs further using the position of the offset, that is front or back as a reference point. So Au would then be back up gliding and Ea front down gliding. By the way, never forget the word diphthong exhibits the letter H twice.