"past continuous tense" vs "would + infinitive"

Question

First example:

1. Maria thought John was going to invite her to the party.
2. Mary thought John would invite her to the party.

Second example:

3. They thought the film was going to start at 8:00.
4. They thought the film would start at 8:00.

What is the difference in meaning between the "past continuous tense" and the structure "would + infinitive" when we are talking about past expectations and beliefs using the verb "think"?

Answer 1

Although seemingly synonimous, these two uses can have different meanings.

In your examples, the first sentence expresses planning while the second one shows a general expectation/ promise.

First example:

1. Mary thought John was going to invite her to the party -> She thought he planned to invite her; she was on his guest list.

2. Mary thought John would invite her to the party -> She saw it as a logical, reasonable expectation that he did. expectation/ promise ( because they are good friends or because he said he would)

Second example:

3. They thought the film was going to start at 8:00.-> They thought the film was scheduled to start at eight. - plan
4. They thought the film would start at 8:00.-> They were told/they assumed that that was the time it started. - expectation/promise

Check some more examples and explanation of future in the past in this page if you like. It's no grand authority as such, but there is some helpful information.

Answer 2

They are synonymous in this case.

If we talk about the future we can say:

"I think John will invite me..." "I think John is going to invite me..."

For these predictions we can use both "will" and "going to"

Your sentences are 'future in the past', and in that case, "will" becomes "would", and "is going to" becomes "was going to"