Re: 1 + 1 = 2
Peter Soderqvist said:
If you have one abstract unit, and add one equal abstract unit to it, you have two of them, is that sum sometimes wrong?
Yes. For example, if I have a lump of mud and stick another lump of mud to it, I don't have two lumps of mud; I have a single, larger, lump of mud. (If you don't like mud, I can do the same thing with a lump of peanut butter.)
If I have a cold room and I add a space heater to it, I get a warm room. If I add another space heater to it, I don't get two warm rooms -- or even necessarily a warmer room.
If I have one happy cat on my lap, and someone adds another happy cat on my lap, I probably now have
zero[ happy cats.
And if I have a cup of water and I add a cup of alcohol to it, the resulting solution isn't two cups of liquid.
Of course, if I have a brick and add another brick to it, that does indeed make two bricks.
But why should our hypothetical "abtract units" be defined to -- or indeed,
self-evidently have the properties of bricks, instead of lumps of mud or happy cats?
Is this proposition not always truth; "System P is consistent if G is not provable within P"?
Yes, that proposition is sometimes incorrect. For example, I can develop an inconsistent system where the Godel sentence for that system is not even expressible within the system, and therefore not provable.