MikeNovack wrote: ↑Mon May 18, 2026 4:42 pm
Immanuel Can wrote: ↑Mon May 18, 2026 3:30 pm
And we know that from logic: something can be what we call "valid" and still, in the conclusion, be "false," if the premises lack truth in one or the other of the basic two premises.
Justify your assumption.
There's no "assumption," Mike. And it's easy to demonstrate.
All unicorns are black.
Black things heat up in the sun.
Therefore, unicorns heat up in the sun.
The
form of the above argument is correct. The conclusion is false, and it's the fault of the first premise. The first premise contains to untrue things: one is that unicorns "are" not a
real thing but an imaginary one, so can't "be" any particular colour; the other is that the representations of these things are rarely if ever black, and usually white.
So my claim is warranted by the example:
something that has valid structure can still be false, if one of the premises lacks truth.
If the premises lack truth, the conclusions will lack truth.
Not quite.
Here's the correct version:
if the premises are not true, then any true conclusion would be only by accident or error, not by way of logic.
So, for example, I can write two false premises and then arrive at a true conclusion, as in this case:
All unicorns are black.
All black things are unreal.
Therefore, unicorns are unreal.
Now, while it is true that black unicorns are not real, it is not by way of the two premises that I have been able to arrive at that conclusion. Both premises are actually false, and obviously so. And the logical structure is still valid: All A are B, All B are C, therefore, conclusion. That's the right way to form a logical syllogism. But the falsity of the two premises render the conclusion only accidentally, not automatically or logically, true.
So a conclusion may be accidentally true, but the logic being used to produce it not adequate to have led to that conclusion. And that's the sort of example you're probably talking about, I think.