I do! did I?

I do! 

That´s the answer everyone is expecting from a bride and a groom as they are about to get married. But, what does this use of the auxilary mean?
Have a look at the following scene from a very popular film where "I do" is used and the auxiliary becomes a powerful language tool. 
 

Here you have the lyrics from the video: 

PRIEST: Donna, do I take the wedding is cancelled…?

DONNA:I´m not… entirely sure what´s happening right now 

SAM: Hang on! Why waste a good wedding? How about a certain…? You are going to need someone to boss around in this island of yours. 

DONNA:Are you nuts? I am not a bigamist

 

SAM:Neither am I. I am a divorced man who´s loved you for twenty one years and ever since the day I set foot on this island I´ve been trying to tell you how much I love you. Come on Donna, It´s only the rest of your life!

SAM:I can't conceal it. Don't you see? Can't you feel it? 

GIRLS (Pause): Say I do, I do, I do, I do, I do (1)

SAM: Donna, please show it. You love me, and you know it. 

GIRLS: Say I do? 

DONNA (Pause): I do, I do, I do, I do, I do: (2)

Now, what does the "I do" mean in this video? The right answer is that it is just substituing a whole statement: "I love you". You should also notice that there is another auxiliar being used by Sam: "neither am I" in order to express agreement with Donna´s previous statement. These two different uses of the auxiliaries show two different ways in which auxiliaries can be used to perform functions other than offering support to the main verb. However, there are some more. Have a look at the following list: 
  1. To avoid repetition. I love watching romantic comedies but my girlfriend doesn´t. 
2. To say that someone or something is the same with the use of SO and Neither. I enjoy riding a horse. So do I.  I dont enjoy scary films. Neither do I 
3.  To say that someone or something is different. My sister studies at University. I don´t. 
4. To show interest or surprise. I go diving every summer. Do you? 
5. To show emphasis. I thought you did not like dogs. I DO love dogs. 
6. To make question tags. (seeking for agreement, confirmation or questioning). It´s a nice day, isn´t it?

Now, which of these functions does the "I do" from weddings perform? Well, if you have answered number 1, you are right. When the priest asks the bride and groom: do you take this man/woman to be your husband/wife?, the bride and groom are expected to answer "I do" in order to avoid repetition of the previous sentence. 
Finally, a brief note about some of the terms from the lyrics that you may find more difficult to understand (in bold):

• Boss around:  to give orders to someone in an unfriendly way.
• Be nuts (slang):  to be crazy
• Bigamist (adj): someone who is married to more than one person
• Set foot on (somewhere):  To arrive at a place
• Conceal: hide some information or knowledge 

Now, you like my blog. Don´t you? I hope you say: "I do!" 

Have a lovely weekend!