Deductive vs Inductive Reasoning FLOW CHART | Valid, Sound, Strong, & Cogent

Introduction to Logical Arguments

  • Overview of logical argument types: deductive vs. inductive, valid vs. invalid, strong vs. weak, sound vs. unsound, cogent vs. uncogent.

  • Understanding the relationship of different logical concepts is crucial for evaluating arguments.

Key Questions in Argument Evaluation

  • Initial question: "What is the aim of the argument?"

    • Deductive arguments aim for guaranteed conclusions.

    • Inductive arguments aim for probable conclusions.

Deductive Arguments

  • Definition: Deductive arguments aim to guarantee the truth of their conclusion based on the truth of their premises.

  • Example of Deductive Reasoning:

    • Premise 1: All squirrels are mammals.

    • Premise 2: This is a squirrel.

    • Conclusion: Therefore, this is a mammal.

    • This argument is deductive because its intention is to clearly demonstrate that the conclusion must be true if the premises are true.

Inductive Arguments

  • Definition: Inductive arguments seek to show that their conclusion is likely true, based on their premises.

  • Example of Inductive Reasoning:

    • Premise 1: Grizzly bears have not been seen in these parts for many years.

    • Conclusion: Therefore, we should be safe from grizzlies while hiking on this trail.

    • This argument is inductive as it does not provide a guaranteed conclusion, but rather a probable one.

The Evaluation Process

  • The first level of the logical framework differentiates between aims: guaranteed (deductive) vs. probable (inductive).

  • The second level assesses the success of the reasoning itself based on the intended aims.

Assessing Deductive Reasoning

  • Validity: If the premises are true, does the conclusion have to be true?

    • If yes, the argument is valid. If no, it is invalid.

  • Example of Invalid Argument:

    • Premise 1: Mary's pet is black and white.

    • Premise 2: Penguins are black and white.

    • Conclusion: Therefore, Mary has a pet penguin.

    • The conclusion may not necessarily follow; Mary could have a black and white cat, making this argument invalid.

  • Example of Valid Argument:

    • Premise 1: This puppy is either a Schnauzer or a bulldog.

    • Premise 2: It is not a Schnauzer.

    • Conclusion: Therefore, it must be a bulldog.

    • If both premises are true, the conclusion must be true; thus, this reasoning is valid.

Assessing Inductive Reasoning

  • Is the conclusion probably true if the premises are true?

    • If yes, the argument is strong. If no, it is weak.

  • Example of Weak Argument:

    • Premise: I spotted a Kestrel last weekend while bird watching.

    • Conclusion: Therefore, we'll probably spot one this weekend too.

    • This does not provide enough information to support the conclusion, rendering it weak.

  • Example of Strong Argument:

    • Premise 1: The jaguar is Sally's favorite animal.

    • Premise 2: She enjoys wildlife photography.

    • Conclusion: So she'll probably enjoy this photo of a jaguar.

    • While it’s possible Sally may not like the photo, it is reasonable to believe she would, making this argument strong based on the premises provided.

Truth of the Premises

  • The analysis does not require true premises to classify the argument as valid, invalid, strong, or weak.

    • The reasoning can still hold as correct independent of the truth of the premises.

  • Example of Valid but Ridiculous Argument:

    • Premise 1: All Shar Peis eat bananas.

    • Premise 2: All banana eaters can fly.

    • Conclusion: Therefore, Shar Peis can fly.

    • Although the premises are absurd, the reasoning is valid since true premises would lead to a true conclusion.

Errors in Arguments

  • Two primary ways an argument can fail:

    • Weak reasoning: premises do not effectively support the conclusion.

    • False premises: reasoning can be flawless but still based on falsehoods.

Testing for Soundness

  • Validity alone does not determine the argument's strength; premises must also be true for soundness.

    • Example: Valid but Unsound Argument

    • If the premises are false: the argument is valid but unsound.

    • Example: Sound Argument

    • A valid argument with true premises is considered sound.

Inductive Argument Soundness

  • For an inductive argument to be cogent (strong with true premises):

    • It must present strong reasoning and be evaluated based on the truth of its premises.

    • Example of Not Cogent Argument:

    • The jaguar argument, while strong, had premises which were not true (hypothetical). Thus, it is strong but not cogent.

  • Example of Cogent Argument:

    • The bear argument provided real premises: the last Grizzly sighting was in 1924 in California.

    • Hence, it is cogent as it provides both strong reasoning and true premises.

Conclusion

  • The logical flowchart provides an organized method to assess and classify arguments effectively.

  • Understanding the distinctions between deductive and inductive reasoning, as well as valid vs. invalid and strong vs. weak arguments, is foundational to the study of logic.

  • Recommended to explore additional resources for a deeper understanding of the fundamentals of logic and argumentation evaluation.

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