We continue our discussion of Metaphysics with the topic of Identity.
Leibniz's Law - If A has all the same properties B has, and B has all the same properties A has, then A = B; less technically, if two objects have all the same properties in common, then these two objects are identical; or two objects are the same if and only if they share all the same properties.
For example, if the Morning Star has all the properties Venus has (is the 2nd planet from the Sun, is very hot, etc.) and the Evening Star has these same properties in common, then the Morning Star is the Evening Star. They both are identical; more precisely, they are physically identical. It simply turned out people were calling Venus by two different names depending on the time of day.
Two things could have many of the same properties in common, such as "identical" twins. They both have the same parents, the same bone structure, etc. However, they have some properties they do not have in common, such as personality or fingerprints. Therefore, Leibniz's Law tells us that "identical" twins are NOT technically identical. They are merely similar.
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Here's a link to a webpage that explains the basics of Logic and deductive standards (or deductive arguments) in good detail, please read through it!
http://kristopher.g.phillips.googlepages.com/logicprimer
Email me with any questions you might have, or see me during office hours!
