1. He won the first prize in the speech contest.

2. He won first prize in the speech contest.

3. He got the first prize in the speech contest.

4. He got first prize in the speech contest.
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Are all the expressions grammatical? Do we have to use 'the' or not? Is either OK? Which one is commonly used, with 'the' or 'without 'the'?

All four are grammatically correct, but using "won" and not using "the" are smoother, more commonly used expressions, I think.

Writeacher is correct, but to be, perhaps, a little clearer, the best sentence is #2, "He won first prize..."

All four expressions you provided are grammatical and can be used to convey the same meaning. However, there are slight differences in how they are constructed.

1. "He won the first prize in the speech contest." Here, "the" is used before "first prize" to indicate a specific prize that was won in the speech contest.

2. "He won first prize in the speech contest." In this variation, "the" is not used, but the meaning remains the same. It implies that he won the primary or top prize in the speech contest.

3. "He got the first prize in the speech contest." This sentence is similar to the first example, indicating that he specifically received the first prize in the speech contest.

4. "He got first prize in the speech contest." Just like in the second example, "the" is omitted, but the overall meaning is unchanged. It conveys that he obtained the primary or top prize in the speech contest.

Both versions, with or without "the," can be considered correct and grammatical. The choice between them often depends on personal preference or style. However, in everyday usage, it is more common to omit "the" before "first prize" (as in examples 2 and 4), making these variations slightly more frequently used.