Why is there an upside-down question mark at the begining
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The upside down question mark (¿) is a punctuation mark that is standard in Spanish. If you think about it, it is reasonable and helpful to anyone reading a sentence. It alerts the reader that the sentence is a question before they begin to read.
That is simply proper Spanish punctuation. It allows a reader to know the following statement is a question. The same goes for the exclamation point because it allows the reader know that the upcoming statement is an exclamation. I believe the proper term for these upside-down punctuation marks is "inverted".
¿ - The inverted question mark
¡ - The inverted exclamation point
Also, one of my Spanish teachers once said that it can act like the word "do". You know how in English we say, "Do you want to go to the store?" Well, there really isn't a "do" for Spanish.
"Do you want to go to the store?" ---- "¿Quieres ir a la tienda?"
"I want to go to the store!" ---- "¡Quiero ir a la tienda!"
In English, when a sentence begins with "Do you...", you immediately know it is a question because of that auxiliary "do", but Spanish does not have such an auxiliary, so you wouldn't know it is a question until you reached the end of the sentence and saw the "normal" question mark:
Quieres venir = You want to come
Quieres venir? = Do you want to come?
Also, while statements have the subject first (e.g. you) and then the verb (e.g. have), in questions the order is reversed: "Have you...?" In Spanish this inversion is common, but not compulsory, plus the subject pronoun is normally omitted, so both "you have" and "have you" would look like "tienes". In other words, again, unless you can see the end of the line to check for a question mark, you are clueless in most sentences about the kind of sentence you are dealing with. The inverted question mark provides this information in the absence of the clues you get from the intonation when you hear the language.
Also, it allows you to raise the intonation at any point in the sentence, rather than having to guess where.
You might also ask "Why is there a question mark at the end of a question in English?" A number of languages get along just fine without any overt punctuation for questions.