⚡️ "Once a week" or "once per week"? #DoubtsForLater My students often bring up questions that I can't answer fully at the moment, so I save them and do research later. We don't know everything, do we? Me: What's the difference between "once a week" and "once per week"? GG: There's no practical difference between "once a week" and "once per week." Both phrases mean that something happens exactly one time during the week. OK. That said... What does "per" mean? According to the Cambridge dictionary, it means "for each": 🗣 The meal will cost $20 per person. 🗣 The car was traveling at 70 miles per hour (70 mph). 🗣 There are more cafés per square mile here than anywhere else in the country. Oh, another doubt: Me: Can prepositions "per" and "for" be interchanged? GG: No. "Per" is often used to indicate a rate, frequency, or quantity per unit of something. Examples: 🗣 10 miles per hour. 🗣 Once per week. 🗣 2 dollars per gallon. "For" is often used to indicate a duration, purpose, or recipient. Examples: 🗣 Wait for me. 🗣 A gift for you. 🗣 Work for a company.