A critic might argue that all four SLED criteria are necessary for personhood, and since the unborn do not possess the necessary size, level of development, environment, and degree of dependency, they are not persons. But if each of these criteria is invalid on its own, adding them up does not make the critic’s case stronger. Philosopher Christopher Kaczor writes, “An invalid or unsound argument counts for nothing. Such an argument is a philosophical zero, and even an infinite number of zeros never adds up to more than zero.”152 The critic has to present a good argument against the personhood
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