In the explanation, you use Tú when referring to Mamá and Usted when referring to Madre. In the Kwiz, you had a question with “father”. How can we

Question

know whether tu or usted is required.  Could it not be either, depending on the formality, which is not stated?

Accepted Answer

Hola Linda
The examples given for mamá and madre are in a special note where we explain the use of formal usted and the word madre (instead ofmamá) in some rural areas, but as we say in the explanation box, this doesn't reflect the general use. As a general rule, you would use the tú form when speaking to your mum and dad. 
I hope this helps.
Un saludo
Inma

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Muchas gracias!

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Señor, ¿puede usted firmar aquí, por favor?hi why we use firmar after usted not firma

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When in an informal bar or in a not too posh restaurant, should I use "usted" or "tú" when talking to a waiter or waitress? (In my case: no doubt they will be mucho más younger than I am!)

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Hola IenThere is no 100% correct answer here - usually, if the waiters are young you can confidently use the informal tú - but if it is a posh restaurant you may want to use the usted even if they are young, because you may think their policy is to treat clients more formally so you may feel you need to approach them a bit more formally too.Some people are "always" very polite and maintain the formality whatever the situation, so it is also a bit personal. Saludos