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1. Arguments by António Paulo Costa

2. An argument is a reason to defend a thesis . To argue is to support a thesis on reasons. Arguments are made up of a proposition, called 'conclusion ', and one or more propositions, called ‘premises’ . The conclusion of any argument is the thesis it is intended to defend; the premises are the reasons that support the conclusion. What is an argument?

3. Premise 1 : If God doesn’t exist, life has no meaning. Premise 2 : But life has a meaning. Conclusion : Therefore , God exists. Example of an argument

4. An enthymeme is an argument in which some premise is omitted (it is used in reasoning but not made explicit). Example of an enthymeme: (P1) God is perfect. (C) Therefore , God must exist. Enthymemes Implicit premise : (P2) Everything that is perfect must exist .

5. Each proposition that makes up an argument, be it a premise or a conclusion, can be true or false , but it is never said " valid " or " invalid ". An argument is either valid or invalid , but it is never said " true " or " false ". There can be valid arguments with true or false propositions; and there may be invalid arguments with true or false propositions. See the examples below. Truth and validity

6. Valid argument with true propositions: (P1) All humans are mortal.  (P2) William is human.  (C) Therefore, William is mortal.  Valid argument with false propositions : (P1) All humans are green.  (P2) My dog is human.  (C) Therefore, my dog is green.  Examples

7. Invalid argument with true propositions : (P1) This is an high school class.  (P2) My name is António.  (P3) We are in Miranda do Corvo.  (C) Therefore, the principal is called José .  Invalid argument with false propositions : (P1) All europeans are portuguese.  (C) Therefore, all asians are chinese .  Examples

8. In a deductively valid argument, the conclusion is a logical consequence of the premises. Thus… … in a deductively valid argument, it is impossible for the premises to be true and the conclusion to be false . Example: «If Simão is in Miranda, then he is in Portugal. If he's in Portugal, he's in Europe. Therefore, if Simão is in Miranda, he is in Europe». Validity rule

9. An argument is called “ sound " when it is valid and has all the premises true. Sound arguments

10. How shall we discuss arguments? To discuss an argument we will have to: Assess the truth of each premise . 🡪 knowledge of the world . Assess the validity of the argument , that is, whether the conclusion logically follows from the premises. 🡪 Propositional Logic techniques Assess whether the argument is persuasive , that is, whether it convinces the intended audience. 🡪 Rethoric techniques