1. Even if the sun were to rise in the west, I would never change my mind.

2. Even though the sun were to rise in the west, I would never change my mind.

3. Even if the sun were to rise in the west, I will never change my mind.

4. Even if the sun were to rise in the west, I could never change my mind.

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Are they the same in meaning?
Can we use 'will' instead of 'would' as in #3? What about #4? Is Sentence 4 right?

All are correct and all mean approximately the same thing. The only slight difference is in 3, in which 'will' means 'never, never, never'!!

Are they the same in meaning?

The four sentences have a similar meaning, but there are slight differences in their implications.

1. Even if the sun were to rise in the west, I would never change my mind.
This sentence expresses a hypothetical scenario where the sun rising in the west is unlikely. It implies that the speaker has a strong and unwavering stance, regardless of any extraordinary event taking place.

2. Even though the sun were to rise in the west, I would never change my mind.
Similar to the previous sentence, this one also presents a hypothetical scenario. However, the use of "even though" suggests that the speaker acknowledges the possibility of the sun rising in the west, but still maintains their steadfast position.

3. Even if the sun were to rise in the west, I will never change my mind.
Using "will" in this sentence suggests a stronger conviction. It implies that the speaker is absolutely certain about never changing their mind, regardless of any extraordinary event occurring.

4. Even if the sun were to rise in the west, I could never change my mind.
Sentence 4 introduces the possibility of a weaker resolve. By using "could," it implies that the speaker is less certain about their ability to resist changing their mind in the face of a highly unlikely event.

Can we use 'will' instead of 'would' as in #3?
Yes, you can use "will" instead of "would" in Sentence 3, but it changes the implication slightly. By using "will," the speaker expresses a rock-solid conviction, asserting that their mind will never change under any circumstances.

What about #4? Is Sentence 4 right?
Sentence 4 is grammatically correct, but it implies a slightly different meaning compared to the other sentences. It suggests that, even when faced with an improbable event such as the sun rising in the west, the speaker is unsure about their ability to resist changing their mind.