Reply To: What did people do before Rashi invented Rashi tefillin?

Up to Rashi’s time, people actually would put on either Rashi or Rabbeinu Tam or both. Rashi finally made the psak that his interpretation of the order was correct and all the rabbonim of that time accepted it. One concept is that both pair were worn, the debate was which pair should be worn first. Chasidim wear both pairs after their wedding. Those who wear only Rashi tefilin are not transgressing anything.