Should / shouldn'tVersión en línea Look at the explanation. por Ángela García 1 Use Should is a modal auxiliary verb.We use "should" to give advice or opinions. 2 Video 3 Tips The basic structure for should is:subject + should + main verbNote that:The auxiliary verb should is invariable. There is only one form: shouldThe main verb is usually in the base form. 4 grammar form 5 Tips for negative There is no short form for should, but we can shorten the negative should not to shouldn't.You should not eat junk food. or You shouldn't eat junk food.