Philosophy and logic. In analyzing the phrase below, 1) is it redundant, 2) is it easily refuted, and 3) what might be its opposite?

1) No. I can't remove any words without changing the meaning.
2) It's not an argument, so whether it can be refuted doesn't make sense as a question.
3) Possible opposites include "alien existence on planet Earth", "alien existence on another planet", "human existence on another planet".

It is incomplete.

It's a phrase, not a sentence. It's complete.
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Hello Randy:

First off, Philosophy and logic is NOT a sentence. Furthermore, there's no verb in human existence on planet Earth.  So, there's nothing to refute.  There's NO action, and NO description, so there's NO opposite.  It's just a collection of words.

excon

Planet Earth is not redundant, because it's not the only planet.  The word 'Earth' also holds the connotation of soil, or dirt.

The proposition is that humans exist on planet Earth, which could mean that humans also exist in other places besides planet Earth, such as on other planets, a position that could be refuted due to a current lack of proof.

An opposite would or could be that humans do not exist on Earth, for example.

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It's a heading, not a sentence.  No one ever claimed it's a sentence.

There's not supposed to be a verb in every phrase.  This particular phrase happens not to contain one.

It's not merely a 'collection of words', as stated above, it's a phrase.  If you're having trouble understanding that concept, the definition of 'phrase' is readily available.  Furthermore, you're absolutely incorrect that 

it has no description, it IS descriptive.

As for an opposite, that's why the words 'might be' are there.  They denote probability, and allow for negative response, which is one of the very few points on which you accurately hit.

Thank you.

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So is it your premise that either the phrase "planet Earth" is incorrect because it's redundant, or is it never used by anyone at anytime and you saw it for the first time when I posted it? Of course I'm not stating that something is correct or incorrect merely based on previous usage, not at all. It just begs clarification of what you're emphasizing ad nauseum here. Had I used just the word 'Earth' or 'earth', without 'planet', there also stands the chance that someone might have taken a similar vein that you took and argued its vagueness, as in the phrase "what on earth . . . "

I don't see the "a" human existence as being accurate to the topic, it's more "the" human existence. Both of us are entitled to interpret it as we see fit without one saying that the other is wrong, I believe.

Excluding for a moment the redundancy or not of using 'planet', what is your take on whether or not the phrase in question is accurate? If human existence is probable on (in?) any place other than the planet on which you and I reside, then "human existence on Earth" has relevance. However, if one were to suppose that human beings as we know ourselves to be do NOT exist anywhere other than this planet, then the phrase should probably read, "human existence". The differences are found in the example of human existence on a particular island or a particular continent. Since there are more than one island and more than one continent, and humans can be found on various islands and on all of this planets continents, it's a specific reference to the island or continent being discussed.

Boiled down, I asked whether or not it's necessary to pinpoint planet Earth as the location where humans exist.

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