Present Continuous vs To Be Going To (Future)

[davidsordia]

Hi,
Can anybody help to clarify the difference between the two?
according to Raymond Murphy:
'' We use I am doing(present continuous) when we say what we have arranged to do- for example, arranged to meet somebody, arranged to go somewhere: i am meeting Ann this evening; I am leaving tomorrow. I've got my plane ticket.

we use I am going to do something (to be going to) when we say what we have decided to do(but perhaps Not arranged to do it) : I am going to clean my shoes(i've decided to clean them but i have not arranged to clean them); I am going to look for somewhere else to stay(I have not arranged it).''

Now,once this is clarified, later in his units I think there is something contradicting. have a look:
'' Paul: Liz, i need somebody to take me to the airport tomorrow morning.
Liz: That's no problem. I will take you. what time is your flight?
Paul: 10.50
Liz: Ok, we will leave at about 9 o'clock.
Later that day, Joe offers to take Paul to the airport.
Joe: Paul, do you want me to take you to the airport?
Paul: No, thanks,Joe. Liz is going to take me. ''

I've got a feeling, that from the above, Murphy contradicts the definitions given at the begining. As we can see from the conversation it is clear that Paul and liz made an arrangement. Now, why To be going to if we have arrangements here? does not he say that we use present continuous for arrangements and to be going to for our decisions but perhaps not for arrangements? I am quite unclear about this particular detail.

Can anybody comment on this?

[Harry Smith]

I'd advise you to buy Michael Swan's "Practical English Usage". For Your question open it at pages 186 -195.It'll be a great help to you.

[Tdol]

There's a bit of a grey area where we could use either. The present progressive puts more emphasis on the appointment, the arrangement, etc. In the example, you could easily say 'is taking' as you have made the arrangements. These distinctions are no so much fixed categories as on a sliding scale, merging rather than changing clearly according to whether an arrangement has been made or not. They can be affected by the speaker's atitude, the importance of the arrangement, etc. The same is true of will/going to- there are many cases where either form could be used, somteimes interchangeably and sometimes expressing a slight difference in meaning.

In this case, flights have tickets and things, while lifts are arranged by a phonecall. Not all arrangements are equal.