As a beginner, I am not quite sure about the difference between an assimilating prefix like sub- su- sus- and a prefix plus a connecting vowel. In reference to aut-, auto-, I assume that auto- is aut + o. So does an assimilating prefix always just either change a consonant or get shorter? I understand that a connecting vowel is added and connects morphemes, but since I cannot yet run the Reak Spelling discs, I just want to make sure I am understanding the difference between the two. Thanks for clarifying.