1. Roses are flowers.
2. Some flowers fade rapidly.
3. Therefore, some roses fade rapidly.
Clearly it is logically invalid but it appears logical because it accords with our knowledge of the world — that some roses do fade rapidly.
The logical validity of a conclusion depends entirely on the premises, not on whether the world is some particular way. The statement “some roses fade rapidly” may be true in reality but it does not logically follow from the two premises, and therefore it is logically invalid.
OK, try this. Is this a valid logical argument?
1. Rolls-Royce cars are cars.
2. Some cars are cheap.
3. Therefore some Rolls-Royce cars are cheap.
This more clearly appears to be logically invalid because we know that RR cars are never cheap. But it’s the same argument as the roses argument. Both are equally logically invalid but one appeals more to our intuition than the other.
I bring this up because I wrote a piece in which I argued that our intuition about how the world works is usually wrong because our species evolved in a different sort of world. Check out this post — Our out-of-date Instincts — in the blog for the “How the world works” course.
This is an ask-me-anything post. So what’s on your mind?