sentences:  A number of rules have been determined that specify which consonants can occur together, and in which order.Basically, the consonants with the highest sonority (") are nearest to the vowel, and the ones with the lowest sonority such as plosives are furthest away, notwithstanding certain exceptions such as thorn clusters.Sometimes new roots were created in PIE or its early descendants by various processes such as root extensions (adding a sound to the end of an existing root) or metathesis.