I know this is math, I just do not know what kind.

Original:
All planets are round. Earth is a planet. Thus, Earth is round.

New:
All planets are round. Earth is round. Earth is a planet.
Why is this not a good reasoning?
I know, you can say a ball is round and a ball isn't a planet, but what is the true name for this?

Question

I know this is math, I just do not know what kind.

Original:
All planets are round. Earth is a planet. Thus, Earth is round.

New:
All planets are round. Earth is round. Earth is a planet.
Why is this not a good reasoning? 
I know, you can say a ball is round and a ball isn't a planet, but what is the true name for this?

agent0smith · Answer

This is logic.

I forget the actual name of this particular statement, though

lukecrayonz · Answer

I know :( I don't think it has anything to do with inverse and converse and contrapositives but it might..

anonymous · Answer

If I remember it is called a logical consequence, and in order for it to be true it has to go in a certain order. I think it would fail by saying the Earth is round, wouldn't you have to say the the earth is a planet to conclude the earth is round?

anonymous · Answer

Just because the earth is round doesn't mean it is a planet from what you first said, I could say

All planets are round, a football is round, therefore a football is a planet

It doesn't make sense

lukecrayonz · Answer

"The main principle is that statements in the premises should directly connect with one another. If the connection between premises statements is logically "loose," the argument is weak."

lukecrayonz · Answer

That's what I found. Was just a question because I was thinking about it. Thanks :-)

phi · Answer

see https://en.wikipedia.org/wiki/Fallacy_of_the_undistributed_middle