Using "need" as a modal

Question

consider:

Changes need only be small to make the proposal acceptable.

Q1 : Does it mean it only requires the changes to be small (It is suffice to make the proposal acceptable) or It asserts changes must be small otherwise, the proposal will be rejected?

Q2: Does the modal "need" have the same meaning as "must" ? If they have differences, I will be happy to know them.

Thanks.

Answer 1

Q1: It means the first: it only requires the changes to be small. It is the same as saying:

Changes only need to be small to make the proposal acceptable.

Q2: The modal "need" generally means the same thing as the non-modal "need", showing obligation; it is just another grammatical way of using the word.

On the topic of "need" as a modal verb, it is not generally used in everyday speech, but it isn't very uncommon in formal speech and writing. It is usually accompanied by a negative word or phrase or used in a question, like the following:

Need he leave?

He need not leave.

No one need come.

Note that "need not" can be contracted to "needn't", and "don't" or "doesn't" aren't used.

Modal "need" has no simple past, but a form of the past can be used with "needn't have" which is used to indicate unnecessary events.

She needn't have brought an umbrella. (Perhaps it didn't rain)

Note that you can't use modal "need" with -ing forms.

His beard doesn't need shaving. NOT *His beard needn't shaving.

Using "need" with "only" like this is another way to use modal "need", but in general it should not be used in situations not previously mentioned.

They need to go home. NOT *They need go home.

Answer 2

Changes need only be small to make the proposal acceptable.

Let me rearrange the sentence.

In order to be acceptable, only small changes are needed.

So at least small changes are needed to make the proposal acceptable, but larger changes (above and beyond the needed ones) would be acceptable too. "Needed" meaning required.