Deductive reasoning - Intro to Psychology

Udacity

23 Feb 201501:08

Summary

TLDRThe video explores deductive reasoning through examples. The first example demonstrates valid deductive logic, concluding that all objects create gravity based on true premises. It highlights that correct conclusions follow when the premises are true. However, a second example about math shows how false premises can lead to incorrect conclusions, even with a logical structure. This showcases how deductive reasoning can only lead to accurate results when the premises are valid. The video then transitions to Susan for a discussion on inductive reasoning.

Takeaways

🔍 Deductive reasoning starts with general premises and moves to a specific conclusion.
🌀 Premise A: All mass creates gravity.
🔗 Premise B: All objects have mass, leading to the conclusion that all objects create gravity.
✔️ Deductive reasoning leads to a true conclusion if both premises are true.
⚠️ However, deductive reasoning can only lead to accurate conclusions if the premises themselves are true.
📉 Example: Premise A (I don't know math) and Premise B (I can't learn math) lead to a false conclusion (I shouldn't try to learn math) because both premises are false.
⚖️ Even though both arguments follow a similar structure, one leads to a true conclusion, while the other does not.
🧪 Scientists often use deductive reasoning to make predictions based on general goals.
🧐 Deductive reasoning is effective for structuring logical arguments when the premises are correct.
➡️ The next discussion transitions to Susan, who will explain inductive reasoning.

Q & A

What is an example of deductive reasoning mentioned in the script?
-The example given is: Premise A: All mass creates gravity, and Premise B: All objects have mass. Therefore, the conclusion is that all objects create gravity.
Why does the logical conclusion in deductive reasoning have to be true?
-The logical conclusion has to be true if the two premises are true because deductive reasoning ensures that the conclusion follows logically from the premises.
What is the flaw in the second example of deductive reasoning?
-In the second example, Premise A (I don’t know math) and Premise B (I can’t learn math) are both false, which leads to a false conclusion (I shouldn’t try to learn math).
Why is the conclusion in the second example of deductive reasoning false?
-The conclusion is false because both premises are false, showing that the reasoning is flawed even though the structure is deductively valid.
What distinguishes accurate conclusions from inaccurate ones in deductive reasoning?
-Accurate conclusions come from true premises, while inaccurate conclusions arise when the premises are false, even if the reasoning structure is valid.
What type of reasoning do scientists use when making predictions for general goals?
-Scientists use deductive reasoning when making predictions for general goals.
Can deductive reasoning always lead to correct conclusions?
-Deductive reasoning can only lead to correct conclusions if the premises it is based on are true.
What role do the premises play in deductive reasoning?
-The premises provide the foundational statements from which the conclusion is drawn. If the premises are true, the conclusion must also be true.
How does the structure of deductive reasoning remain the same in both examples?
-Both examples use the same logical structure of premises leading to a conclusion, but the truthfulness of the premises determines the accuracy of the conclusion.
What is the transition made at the end of the script?
-The transition is from discussing deductive reasoning to introducing inductive reasoning, with Susan being mentioned to explain inductive reasoning.

Outlines

00:00

🧠 Understanding Deductive Reasoning

The paragraph introduces deductive reasoning by explaining its structure and logical flow. It presents Premise A: 'all mass creates gravity' and Premise B: 'all objects have mass.' From these premises, the conclusion 'all objects create gravity' follows logically. The paragraph emphasizes that for deductive reasoning to lead to correct conclusions, the premises must be true. The example provided shows a valid logical conclusion based on true premises.

🤔 Flawed Deductive Reasoning Example

This part demonstrates how deductive reasoning can lead to a false conclusion if the premises are incorrect. Using the example, Premise A: 'I don’t know math' and Premise B: 'I can’t learn math,' the false conclusion is 'I shouldn’t bother trying to learn math.' The paragraph highlights that despite the reasoning being logically structured, the argument fails because both premises are false. This demonstrates the importance of valid premises in deductive reasoning.

🔬 Deductive Reasoning in Science

The paragraph briefly transitions to how deductive reasoning is applied in scientific contexts. Scientists use this method to make predictions based on general principles or goals. The text serves as an introduction to the next segment, which will discuss inductive reasoning, teasing a shift in focus to Susan's perspective.

Mindmap

Keywords

💡Deductive Reasoning

Deductive reasoning is a logical process where a conclusion is drawn from two or more premises that are assumed to be true. In the video, it is demonstrated through the example: 'All mass creates gravity' and 'All objects have mass,' leading to the conclusion 'All objects create gravity.' The theme revolves around using general principles to reach specific conclusions.

💡Premise

A premise is a statement or idea that serves as the foundation for an argument or reasoning. In the video, Premise A is 'All mass creates gravity,' and Premise B is 'All objects have mass.' The logical conclusion that follows depends on the truthfulness of these premises, emphasizing that correct premises lead to correct conclusions.

💡Gravity

Gravity is the natural force that attracts objects with mass toward one another. In the video, gravity is used in a deductive reasoning example, where the premise 'All mass creates gravity' leads to the conclusion that 'All objects create gravity.' This illustrates the scientific application of deductive logic.

💡False Premise

A false premise is an incorrect or misleading foundational statement that leads to incorrect conclusions. In the second example in the video, the premises 'I don’t know math' and 'I can’t learn math' are both false, leading to the faulty conclusion 'I shouldn’t bother trying to learn math.' The video highlights that even logically structured arguments can be flawed if based on false premises.

💡Conclusion

A conclusion is the final judgment or decision reached after considering the premises. The video emphasizes that the validity of a conclusion depends on the truthfulness of the premises, as seen in the gravity example, which leads to a valid conclusion. Conversely, false premises lead to false conclusions, as shown in the math example.

💡Inductive Reasoning

Inductive reasoning is the process of drawing general conclusions from specific observations or examples. The video introduces inductive reasoning briefly, signaling a transition to Susan’s explanation of the concept. Inductive reasoning is contrasted with deductive reasoning, as it often involves predicting outcomes based on patterns rather than established premises.

💡Scientists

Scientists are mentioned in the video as users of deductive reasoning to make predictions based on general goals or principles. This highlights the application of deductive logic in scientific methodology, where conclusions are derived from known laws or hypotheses.

💡Logical Structure

Logical structure refers to the organized framework of an argument, consisting of premises leading to a conclusion. The video presents two examples, one leading to a true conclusion (about gravity) and the other to a false conclusion (about learning math), demonstrating how the same logical structure can yield different results based on the truth of the premises.

💡Accurate Conclusion

An accurate conclusion is a final statement or decision that is correct, given the premises are true. The video’s example about gravity leads to an accurate conclusion because the premises are based on true scientific principles. This concept underscores the importance of sound premises in achieving valid conclusions.

💡False Conclusion

A false conclusion is a decision or judgment reached from incorrect premises. In the video, the statement 'I shouldn’t bother trying to learn math' is a false conclusion drawn from two false premises. This illustrates how flawed reasoning can lead to incorrect beliefs or decisions, even if the argument appears logically sound.

Highlights

Premise A: All mass creates gravity.

Premise B: All objects have mass.

Conclusion: All objects create gravity.

Deductive reasoning: If premises are true, the conclusion must be true.

Deductive reasoning can lead to correct conclusions if general premises are true.

Example of false premises: Premise A - I don't know math.

Example of false premises: Premise B - I can't learn math.

False conclusion: Therefore, I shouldn't even try to learn math.

False premises lead to inaccurate conclusions.

Deductive reasoning: Same structure can lead to true or false conclusions depending on the truth of the premises.

Accurate deductive reasoning relies on valid premises.

Scientists use deductive reasoning to make predictions for general goals.

Deductive reasoning is critical for scientific predictions.

The example of reasoning about math demonstrates the importance of premise accuracy.

Transition to Susan for inductive reasoning discussion.