I don’t advise it but there are always exceptions. The course is developed in a linear fashion, meaning that each module builds on the information presented in the previous one. If you do both volumes at once it would be like taking 7th grade and 12th grade classes at the same time. Unless you have the lessons from 7th grade down, you’re most likely going to have trouble and there will be lots of confusion with 12th grade. Now, like I said initially, there are always exceptions to every rule! If you consider yourself a fairly advanced player and understand and can play most of the stuff in vol 1, but just want to have it handy as a reference…then it might work.