Csc 165 week 3: Conjunction, disjunction, negation, implication

One of the more interesting things we went through this week in lecture was negation. As a general rule of thumb existential can be negated to universal and vice versa. A implies B is negated to A and not B. Thinking about negation in human language helps with the visualisation and understanding of the concept. The concept sounds like it will be easier to understand after more practice.

Truth tables on the other hand is a relatively harder concept for me to understand.it is a little hard to follow when we say P implies (Q implies R). does it mean that when P is true it implies that Q implies R is true which would mean that Q needs to be true to imply R is true. it took a while but eventually i realised that looking at it backwards is easier. In the sense that if R is true and Q is true statement Q implies R is true thus if P is true whole statement will thus be true.

In tutorial one person brought up the point that the statement 'only if''is technically the same as the statement 'if and only if' in the sense that lets say if we say a person resigns only if he is exposed to the media. Then at lest from the the point of human language exposing him to the media would imply he resigns and since he only resigns if he is exposed to the media the reverse is also true. however I would argue that this is due to the nuances in the human language which contributes to the misunderstanding. we can also say that there will be a rainbow only if it rains. Here a rainbow would imply it rained but the reverse in this case is not true since raining will not guarantee a rainbow. thus I think it would be better to not rely too much on the human language in cases like this and assume only if is an implication in one way.The debate on this subject made the tutorial a lot more interesting then it was last week. hopefully we'll have another spirited debate in tutorial again next week.