Disjunction (do not confuse with disjunctive syllogism) today, we will add one more method to our rules of valid inference. this rule is called disjunction, abbreviated disj. this is not the same as ds, which stands for disjunctive syllogism this rule means that from a simple premise such as "i am a human being" we can derive a conclusion that "i am a human being or a bird." why would i want to derive such a useless and perhaps a silly conclusion? well, because this addition will not change the truth of my statement and it will prove useful. so: from: h i can derive hvb from: i can derive p vq from a i can derive a v b and so the premise h, in the first example, is true. it states that "i am a human being." which is true. now, i am of course not a bird, but the sentence "i am a human being or a bird" remains still true even if it is not true that i am a bird. so technically i can create a conjunction from any single premise and that will not affect my true statement