The main argument put forward in favour of altering the definition of marriage as being between a man and woman is that this discriminates against relationships between individuals of the same sex and hence constitutes a violation of their right to have their relationship recognised as having equal value.
In short, the argument is that it devalues their love.
The question I want to examine is whether this is a sound argument.
One way of encapsulating the logical form of the argument is the following:
1.All love between all persons is equal (Assumption – that is, an assertion that is taken as given).
2.Love is recognised through marriage (Assumption).
3.Marriage is a human right (Assumption).
4.Human rights apply to all human beings (Assumption).
5.Marriage is a human right of all human beings (from 3 and 4).
6.Love between gay individuals is equal to other forms of love (from 1).
7.Love between gay individuals is recognised through marriage (from 2 and 6).
8.Marriage between gay individuals is a human right (from 5 and 7).
The question now becomes one of determining whether the argument is sound, since it appears to be a valid argument – that is, assuming the premises from which it begins are true, the conclusion is true. On the other hand, if any of the premises are false, then the conclusion is false, though the argument is still valid (since the form of the argument is valid). It is another matter whether the argument is sound. It is not sound if any of the premises are false, since the conclusion will not be true.