16th century German philosopher Gottfried Wilhelm Leibniz is often credited as being the first philosopher to posit the principle known as the Identity of Indiscernibles (Loemker 1969: 308). This principle states that if x has exactly the same properties as y, then x is identical to y. An interesting consequence of this principle arises from the implication that no two objects have all of their properties in common, since such an implication suggests that perfect duplicates cannot exist. Perhaps the most famous opponent of the Identity of Indiscernibles is Max Black, who argued against the truth of this principle in his essay “The Identity of Indiscernibles” by postulating a world in which two exactly similar spheres (perfect duplicates) could exist. In this paper, I shall argue against the Identity of Indiscernibles by defending Black’s claim that perfect duplicates can exist. Our discussion will be focused on the argument below.
(1) If the Identity of Indiscernibles is true, then there cannot be perfect duplicates
(2) There can be perfect duplicates
(3) The Identity of Indiscernibles is false Often, two objects are referred to as indiscernible if and only if they share exactly the same properties. However, one must be cautious of such a definition of indiscernibility because of its ambiguity. According to the Identity of Indiscernibles,
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As Black says, “every quality and every relational characteristic of the one [sphere] would also be a property of the other [sphere]” (156). Since Black’s alternate universe contains two entities that have all and only the same properties in common, it appears he has created a world in which the Identity of Indiscernibles does not hold because this world permits the existence of perfect