 Hello and welcome to the session. In this session, we are going to discuss the validity of an argument using logic. An argument consists of a set of statements called premise which leads to a conclusion. So we may define premise as a proposition which is true or expected to be true. And conclusion may be defined as a proposition that is derived from premises. Now we will discuss law of detachment and law of syllogism from where we can draw valid conclusions. First let us discuss the law of detachment. It includes a true conditional statement in if p then q form. If conditional statement is true and p is true then q is also true. That is if the conditional statement and p are true then the conclusion q is also true. Symbolically it is written as p implies q and p therefore q. Here the premises are p implies q and p and the conclusion of the statement is q. So from statements p implies q and p we are implying conclusion q. Symbolically it can be written as premise 1 is p implies q, premise 2 is p, the conclusion is q or p implies q and p therefore q. Consider the following statements. First if measure of an angle is less than 90 degree then it is an acute angle. Second measure of angle a is less than 90 degree. What conclusion can be drawn from these statements? Here premises are if measure of an angle is less than 90 degree then it is an acute angle and measure of angle a is less than 90 degree. So we conclude angle a is an acute angle. We can write it as if measure of an angle is less than 90 degree then it is an acute angle and measure of angle a is less than 90 degree therefore angle a is an acute angle. Now let us discuss law of syllogism. It is an argument consisting of three statements p, q and r. The third statement is the conclusion drawn from the first two statements. It is represented in the following way. Premise 1 is p implies q, premise 2 is q implies r, therefore conclusion is p implies r. If p implies q and q implies r are true then p implies r is also true. Consider the following statement. If Jane gets good marks then she can go out to watch a movie. If she goes out to watch a movie then she will see her favourite star. Now we will draw a valid conclusion from this statement. Here we have p, Jane gets good marks, q she can go out to watch a movie or she will see her favourite star. So here premise 1 is if Jane gets good marks then she can go out to watch a movie. Premise 2 is if she goes out to watch a movie then she will see her favourite star. Therefore conclusion is if Jane gets good marks then she will see her favourite star. Other types of valid arguments are law of contraposition which is represented in the following way. Premise 1 is p implies q, premise 2 is not q therefore not p. Next is law of disjunctive syllogism which is represented as premise 1 is p or q, premise 2 is not p therefore not q. So in this session we have discussed law of detachment, law of syllogism, law of contraposition and law of disjunctive syllogism. This completes our session. Hope you enjoyed this session.