Like maths equations, logic has a structure.
It looks a bit like: one, plus two, equals three. On one side of the equation we
have things we already know or agree upon.
On the other side is an answer that's true, so long as the numbers on the other side
don't change.
In logic, an idea is called a premise, which can be put together with other
premises in such a way that they lead us to a conclusion.
One premise might say magnets attract iron,
the other premise might be, this object is made from iron. Without seeing it
you can logically say that the magnet will attract this object.
But what if you swap around the information? Say, magnets attract iron and this object
is attracted to magnets.
Can you then say that this object is made from iron?
Unfortunately not. It still looks like logic but the conclusion no longer works.
Magnets not only attract iron, but other metals as well, such as nickel.
This broken logic is called a logical fallacy.
This particular example, is a formal fallacy. Because its form looks similar
to logic, but is false. In Latin and in legal circles, it's called a 'non sequitur' which
means 'does not follow.'
It's easy to mistake a logical fallacy for the real deal if you're not careful.
People do it all the time. Sometimes by accident and sometimes to fool you.
Knowing the structure of a logical argument is important. You wouldn't make the
mistake of thinking: three, plus two, equals one.
Rules are rules after all.
But breaking the rules of logic, can make an answer seem right,
when it isn't.