1. I have been there already.

2. I have already been there.
3. I was already there.
4. Already I was there.
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Are they all grammatical? Which ones are commonly used? Do we have to use the present tense or the simple past tense?

All are grammatically correct. Only #4 is awkward. The adverb would be better placed at the end of the sentence in #4.

Either tense works fine.

All four sentences are grammatically correct, but the order and usage of words may vary depending on the intended meaning and emphasis. Let's analyze each sentence.

1. "I have been there already." - This sentence uses the present perfect tense ("have been") to indicate that the action of going there has happened before the present moment. "Already" is used as an adverb to emphasize that the action occurred in the past.

2. "I have already been there." - This sentence is similar to the first one, but it places the word "already" before the main verb "been" to enhance the emphasis. The use of the present perfect tense remains the same.

3. "I was already there." - In this sentence, the simple past tense is used ("was") to indicate that the action of being there occurred at a specific time in the past. "Already" is used as an adverb to emphasize that the action had already happened by that specific time.

4. "Already I was there." - This sentence is grammatically correct but less commonly used. It places the adverb "already" at the beginning of the sentence for added emphasis. However, this structure is typically less natural and more commonly found in poetry or literature.

In terms of common usage, the first two sentences are more frequently heard in everyday conversation. The choice between using the present perfect tense or the simple past tense depends on the context and the exact meaning you wish to convey.