Oil and vinegar do not mix well on their own because their molecules do not bind together. So, to make them meld, you need to add a third element to the dressing that both vinegar and oil will ...
My mom and sister think I’m a snob, but I haven’t bought a bottle of salad dressing ... oil or a mild oil, like canola or grapeseed. The word “acid” is a little harsh, but so are vinegar ...