Combining IFs - how do I check for multiple conditions?

Combining IFs - how do I check for multiple conditions?

Since my first question was too difficult, I ask a simpler one

How do I check if two or more conditions are met?

if (!$(this).is('.class1') && !$(this).is('.class2')) {


does not work.
Never mind that I can combine the two classes, I need to check for groups of classes so it'd be like

if (!$(this).is('.class1,.class2') && !$(this).is('.class3,.class4')) {