- Slides: 15
Unit 1 – Foundations of Logic Reasoning and Arguments
�When someone is trying to convince you to act a certain way of believe a particular idea, it is likely that he or she is using an argument ◦ Giving a reason(s) to support a particular conclusion
�Argument: consists of a propositions that the arguer takes as true, with one particular proposition, the conclusion, argued for by using the other proposition, the premises ◦ Arguments are built out of propositions
• Example : Capital Punishment Debate Capital punishment should not be used because wrongly convicted people will be executed by mistake and that is total unacceptable. � Premise 1: if capital punishment is used, then wrongly convicted people will be executed by mistake � P 2: the execution of wrongly convicted is totally unacceptable � Conclusion: capital punishment should not be used.
�Certain words or phrases that typically serve to introduce the conclusion of an argument ◦ Conclusion-indicators Certain words that typically indicate the premise of an argument � ◦ Premise-indicators Conclusion-indicators & Premise-indicators
Conclusion Premise Therefore Since Hence Because Thus Given that So Assuming that Consequently Insomuch as We may conclude that… For the reason that… Common indicators
�Not all arguments includes one of these indicators Example ◦ There is no such thing as free will. The mind is induced to wish this or that by some cause, and that cause is determined by another cause, an so on back to infinity. Spinoza
�The presence of an indicator is no guarantee that there is an argument ◦ Dinosaurs are extinct because of the impact of a large asteroid �The proposition is not being argued it is being taken as true and given an explanation for why it is true
Deductive Logic: �The sudoku puzzle is currently a very popular form of logic game. �The strategy for solving a sudoku uses a reasoning process. �Sudoku puzzles use a form of reasoning called deductive logic. Deductive, Inductive & Abductive
� In deductive logic, you draw inferences (identify relationships) between information you know for certain and information you need to know. You attempt to work towards the point where, if the original information you know-- 'premises'--is true, then the conclusion must be true as well. � In a sudoku puzzle, for example, if you know that a specific square could contain the number 4, 5, 6, or 9, and that on another level the same square is part of a vertical line that cannot contain any of the numbers 4, 5, or 9, then you can conclude that it must contain a 6. If your original information about what the box cannot contain is correct, the conclusion must be correct. Deductive logic allows for absolute certainty.
�Deductive invalid argument is either valid or ◦ Valid deductive argument is one in which the conclusion is logically followed by the premises ◦ Invalid deductive argument is one in which the argument is offered as valid, but the conclusion turns out not to be logically entailed in the premise
�Deductive arguments are a form of syllogisms: 3 line argument in which the first two line are premises and the third line is the conclusion ◦ All men are mortal ◦ Socrates is a man ◦ Socrates is mortal
�Invalid deductive argument ◦ A stone is a substance ◦ Your are a substance ◦ You are a stone ◦ Why is this invalid? �A stone is a substance (does not say all/every substance is a stone) – flawed argument
�Is an argument in which the conclusion is probably true, given that the premises are true. Consider the following: ◦ In a survey of all 1839 students at Hegal high school approx 95%responeded that they believe in the existence of an absolute spirit ◦ Gottfried is a student at Hegel high school ◦ Gottfried believes in the existence of an absolute spitit Inductive arguments
�Is one in which the conclusion is a ‘best guess’ that is judged to be the most plausible explanation among competing alternatives, given that the premises are true. ◦ If it was raining last night, then the street will be wet. ◦ The street is wet ◦ It was raining last night �Can be true or false but that is the best guess Abductive Argument