I found this picture helpful. It shows difference between the fit of 4 classic pant styles.

1) Cullotes – hangs away from the body at abdomen and buttocks
2) Trousers – hangs straight from the fullest point at buttocks and abdomen
3) Slacks – cup slightly under the buttocks and abdomen
4) Jeans – follow body contours very closely.
This picture helped me to visualize how to alter one pattern to get 4 different pant foundations. Once I have those fitted, I can further change leg lines and hems. Shorts are based on one of the four pant foundations as well.