What is the difference between は and が in this sentence?

Question

This is an example sentence from a set of learning materials called Kanji Odyssey 2001:

北極にはシロクマなど陸上の動物がいる。南極には陸上の動物はいない。

My question is about the bold. I understand the には I think because it is showing contrast between the two locations. I feel like the は at the end has to do with contrast as well... but I don't know? Can you contrast the same thing? And if so why aren't there two は's, why is one a が?

Answer 1

In fact, this は, seldom mentioned in research works, (at least in the hundreds of papers and books I have read), is a little different.

In short, I think it is used to show and show how the statement agrees or disagrees with an existing proposition.

In your example, it clear to see the two sentence are almost the same except the parts before and after は.

北極　にはシロクマなど陸上の動物が　いる。
南極　には　　　　　　陸上の動物は　いない。

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Let's see some more examples of the second は. (I think we don't normally use the verbose form to answer, though.)

A: 　　　　りんごは　好きですか
B: いいえ。りんごは　嫌いです。

A: 　　　　雨が　降っていますか
B: いいえ。雨は　降っていません。

A: 　　　　酒を　飲みますか？
B: いいえ。酒は　飲みません。

A: 　　　　東京に　　止まりますか？
B: いいえ。東京には　止まりません。

A: 　　　　みんなと　　同じですか？
B: いいえ。みんなとは　違います。

A: 　　　　仕事だけが人生で　　　　　すか？
B: いいえ。仕事だけが人生では　ありません？ (actually, ではない is a little special)

A: 　　　　ここから　　見えますか？
B: いいえ。ここからは　見えません。

You may argue that the only contradictory part is the negation part, that is, the ません, ない part. But normally, you don't split a verb(e.g. 行かない→行きはしない), unless you want to emphasize. It's common not to insert a は between a verb or an adjective and its auxiliary verb. In these case, は has to be moved the to the last case particle before the verb, whenever it is possible.

A: 行き　　ますか。
B: 行きはしません。 (expected form, sometimes used)
B: 行き　　ません。(normally used form)

A: 高い　　　ですか。
B: 高くはないです。 (expected form, but may imply different meaning)
B: 高く　ないです。(normally used form)

A: 雨が　降ってい　　ますか？
B:*　　　降っていはしません。 (expected form, but I have never heard)
B: 　　　降ってはいません。 (often used)
B: 　　　降って　いません。 (normally used)
B: 雨は　降って　いません。 (は is moved backward)

妹を　お前には　渡さない。(は is moved backward to に)
行動しない者に、幸福がは　訪れない (は is moved backward to が)

The kind of は can be used in statements, questions, imperatives, and adnominal clauses,

酒は飲みません。
そうは思いませんか？
冗談はほどほどにしなさい！
人とは違う道

while it doesn't seem to get along with conditional clauses (ば, なら, etc.), but I'm not sure.

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Many particles like など, なんか are sometimes used instead of or in front of は.

嘘なんかついてねーよ。

As far as I know, it usually safe to use は in sentences containing verbs like ～ない or 違う,etc. For other verbs, an explicit context is usually required to make it natural.

A:異世界は　ないでしょ。 (Containing ない, so no context required. The statement contradicts the common sense.)
B:異世界は　あるよ。 (context required. Contradicts to A's proposition.)

Sometimes は is lightly used to contrast with logically contradictory facts. In this case, they are most like “whereas/but”.

雨が・は降りましたが、傘は持って行きませんでした。 (We normally expect one to take an umbrella with him if it rains, but it isn't.)

Last word about ではない. It's often lightly used instead of でない, so the は may carry little meaning. ではなく and でなく are somewhat interchangeable. The difference is even neutralized if you use じゃない. So in the following example, you see は is used twice.

A: あなたはりんごが　好きで　　　　すか？
B: いいえ。りんごは　好きではありません。
B: いいえ。りんごは　好きじゃありません。

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I examined the most common case particles like が, を, に, へ, から, と and で, and believe they are obligatorily followed by は in many situations. (see above)

そう is a little different. そう思いません is used as well as そうは思いません. But そうはいかない seems more common than そういかない, but I'm not sure.

Both まで and までは often contain an semi-negative sense. Adverb suffix に, く and と are not used with this type of は, either, except when they are used with verbs like なる, 見える, etc.

For other case-marker-like structures like について, において, にとって, ために, etc. I feel this kind of は is not often used with them. But I haven't investigated on them, so it's just a speculation.

This kind of は is not used with other adverbials.

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Depending on your intent and where you put your stress, same は can often be used to introduce a semi-negative or reticent sense. e.g.

高くはない（が低くもない)

A: みんな行きますか
B: 私は行きます。 (For others, I don't know.)

I think these two types of は are somewhat complementary.

Answer 2

It is more a comment than an answer but since I lack reputation so as to write a comment I write it as an answer.

In fact, you can also use が in the second sentence but (as you guessed) は stresses the fact that there are land animals at the North Pole but at the Southern Pole there are not.

The particle が in the first sentence is just the subject particle が used to introduce your subject 陸上の動物 land animals, here が cannot be replaced by は because the subject has not been introduced yet.

Answer 3

As you say は is used for contrast. It also places emphasis on what comes after it. In this sentence the writer is placing emphasis on the absence of land animals such as polar bears from the South Pole as opposed to their presence in the North.

The most highly voted question is very good summary of は and が but for a short explanation relevant to your question I would refer you to the following answer and comments to this question which cemented this for me: What is the difference between でなくand ではなく？

This question from yesterday might also be of interest: Particle は replacing を - where does the stress lie?