phil001notesWeek3complete - Dr Mcs Philosophy 001(1091...

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1091001notesWeek3 © 1 Dr Mc s Philosophy 001 (1091) Lecture Notes, Week 3 © Assignment 2 is due in your tutorial next week. It is on the Net. Assignment 1 is due this week. Recall from last time. Two requirements for an argument to be a good one. (i.e., rationally strong for you) 1. Its conclusion must follow from its premises. 2. Its premises must be reasonable for you to accept. An argument whose premises, if true, would support its conclusion, is called “well - formed”. An argument is well-formed if and only if it is valid or cogent . Validity An argument is valid = if its premises are true, its conclusion must be true. 1. My van is parked where I left it or my van has been stolen. 2. My van is not parked where I left it. 3. My van has been stolen. Cogency An argument is cogent= if its premises are true, they provide reason to think the conclusion is true, but they could be true yet the conclusion false. 1. Most students in this room are under 25. 2. The person in the top left seat is a student in this room. 3. That person is under 25 Whether or not an argument is valid is simply a matter of its form. (Not so, we‟ll see, with cogency, but Feldman‟s examples work.) How do we display the form of an argument? In some cases, we can use sentential logic. 1. My van is parked where I left it or my van has been stolen. 2. My van is not parked where I left it. 3. My van has been stolen. P=My van is parked where I left it Q=My van has been stolen 1. P or Q 2. ~P 3. Q
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