Question:Some people don't have masters degrees, only bachelors and doctorate? When should one do this instead of a bachelors, masters, then doctorate?
Answers:
There are some key differences in which you should do one or the other. First, the pros and cons of PhD vs. Masters
If you go for the PhD, MOST OF THE TIME, you will have your tuition waived and you will get a stipend to live on (you will usually have to be a TA or a RA). The amount of stipend depends on the program you are going into (sciences usually over $20k). For a Masters program, you will likely pay everything out of pocket, through loans, or if you are lucky, you will get a scholarship. When I applied to grad schools this past year, I applied mostly to PhD programs and to some MS programs. For all of the PhD programs, I got full financial support. For the MS programs, I got nothing...well, reduced tuition...they didn't offer Masters students any stipend/scholarship support.
I think I remember you saying a few days earlier you were going into Engineering. It would be fine to just get a Masters in Engineering if you want to work in the industry, but if you want to do research, you will want the PhD to stay competitive. As for getting a Masters before a PhD...if you are a student of science (which you are), you may as well go for the full PhD right away if that is your final goal. My final goal is the PhD, and the departments that I applied to for only a Masters thought I was crazy. One of the departments bumped my application up to PhD saying a Masters was a waste of time. If your job can be done with only a Masters, then that may be all you want to pursue. Also, if you plan to get your Masters in one area, and a PhD in another, then it is also a good idea to stop off and get the Masters first. But in your case, stopping off for a Masters isn't necessary unless you want to do your Masters in another area--or if you aren't sure you want to do the PhD. The program I'm in allows you to drop down to a Masters if you want. A lot of programs are offering that option these days. In humanities though, it is a different story all together. It is considered desirable these days to get your Masters first in the Humanities. But for sciences, if you get a Masters then a PhD, you will be repeating A LOT of the same course work...and it's usually just not worth it.
Good luck!