PHI 1101 Lecture Notes - Lecture 5: Logical Truth, Modus Tollens, Modus Ponens

• School: University of Ottawa
• Department: Philosophy
• Course: PHI 1101
• Professor: Sardar Hosseini

Document Summary

Example: mark has twice as many cats as susan. Susan has three cats; therefore, mark has 6 cats: 2. Argument from de nition - purely conceptual / logical truth. Jackson is a liar; therefore, he doesn"t tell the truth: 3. Categorical syllogism: syllogism (2-premised argument, with each statement starting with all , some , none , or every . Socrates is a human, therefore socrates is mortal: 4. Thursday, october 15, 2015: when evaluating deductive arguments, we can ask two independent questions: (these two questions are independent: false premises, false conclusion = valid, false premises, true conclusion = valid, true premises, true conclusion = valid and sound, true premises, false conclusions = invalid. Informal way of evaluating = imagining a situation where it could be untrue. Formal evaluation: the validity / invalidity of arguments could be determined by showing that they conform to certain forms - if they do, we call them valid.