For example, the modal particles dan, eens, even, maar, misschien, nou, ook, soms, and toch. Ga maar zitten is polite, but can you say ga zitten for a stronger, ruder sense?
Yes, ga zitten can be polite (invitation) or rude (command) only depending on the tone/voice/. The maar is of no consequence for either meaning. You can say : "ga dan nou toch maar eens even zitten" ( invitiation/ familiar ) and the nou dan dan maar eens even, those you call modal particles, mean in fact nothing. But even with the whole range of modal particles it can be said in a commanding threatening way.
When I considered English to be the easiest of the three neighbouring languages to learn it was because English does not have like French ( Italian and Spanish too) these two past tenses: the imparfait and the passé défini. Nor the conjunctif or conditionel. And German has those horrible Fälle and Kasus-Fallendungen. ( but now I saw those tenses wriggle up some difficulties in English too in their own way).
