Japanese grammar?

Question

犬は公園にいます。(inu wa kouen ni imasu)
公園に犬がいます。(kouen ni inu ga imasu)

Is there any real difference in these? Or is it just two ways to say it?

Answer 1

Well, I can say that it's very hard even for Japanese to explain of it.

"は" is a topic marker. Therefore, the noun in front of "は" is a topic in the sentence. It often becomes a subject or sometimes an object.

"が" is a case marker. It often indicate that the noun in front of it is a subject or sometimes an object.

A: Where is the dog? -> 犬はどこにいますか？
B: The dog is in the park. -> 犬は公園にいます。

The dog (犬) is a topic and also subject.

A: What is in the park? -> 公園に何がいますか？
B: A dog ( is in the park ). -> 公園に犬がいます。

A dog ( = what ) is a subject.

Another example for your information.

A: Where is the meat? -> 肉はどこにありますか？
B: The dog ate the meat -> 肉は犬が食べました。

The meat (肉) is a topic. It is a subject in the sentence A, and it is an object in the sentence B.
The dog (犬) is a subject in the sentence B.

Answer 2

1st sentance: The dog, is at the park.

2nd sentance: At the park, there is a dog.

So yes there is a difference. The first sentance, with "inu ha" places the dog as the subject. Where that emphasis is not placed on the dog in the second sentance. The subject of the second sentance is more the park, rather than the dog.

While not a seemingly huge difference, it is still a difference.