SAGE Flex for Public Speaking
1
Lines of Reasoning
Learning Objective: In addition to choosing valid evidence to support their proposition, public
speaker’s need to use logical reasoning to develop persuasive arguments.
Learning Objective: Dete rmine if a persuasive speech argument is logically sound.
Key Terms:
• Deductive reasoning: A kind of reasoning in which you surmise specific examples
from general propositions.
• Inductive reasoning: A kind of reasoning that constructs or evaluates general
propositions that are derived from specific examples.
• Syllogism: An inference in which one proposition (the conclusion) follows
necessarily from two other propositions, known as the premises.
What Makes an Argument Logical?
Reasoning is consciously making sense of things, establishing and verifying facts,
applying logic, and changing or justifying practices, institutions, and beliefs based on new or
existing information.
Logic is a branch of philosophy devoted to understanding how human beings develop valid
arguments by conveying evidence in compliance with logical reasoning. In addition to choosing
valid evidence to support your proposition, you need to use logical reasoning to develop your
persuasive argument.
Deductive Reasoning
Deduction is a form of reasoning in which you surmise specific examples from general
propositions. The term deduction is used for the conclusion reached by a deductive reasoning
process. Deductive reasoning often includes a syllogism, which is a kind of logical
argument that applies deductive reasoning to arrive at a conclusion based on two or
more propositions that are asserted or assumed to be true.
One classic example of deductive reasoning syllogism is as follows:
Premise 1: All humans are mortal.
Premise 2: Socrates is a human.
Conclusion: Socrates is mortal.
The reasoning in this argument is valid because there is only one logical conclusion to these
statements. There’s no way in which the premises, 1 and 2, could be true and the conclusion, 3,
could be false.
