The Prohibition of Contradicting Your Parent

The Gemara says contradicting a parent is a form of disrespect. Included in this is weighing in on a dispute a parent is having with someone else, even if you're goal is to assist your parent. The Shulchan aruch rules that voicing agreement applies in the parent's presence. Is it ever permissible to contradict a parent? How was the Tur able to argue with his father, the Rosh?

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