Master the fundamental building blocks of critical reasoning: propositions, arguments, indicator words, and complex argument analysis.
What is Critical Reasoning?
Much of our daily life is guided by instinct, emotion, or gut feelings. But when we stop to think reflectively about what to believe or how to act, we engage in critical reasoning. According to educator Edward Glaser, this process involves three key elements:
- An attitude of being disposed to thoughtfully consider problems and subjects.
- Knowledge of the methods of logical inquiry and reasoning.
- Skill in applying those methods.
This module focuses on building your knowledge and skill, starting with the most basic components of any logical discussion.
1. The Building Block: Propositions
A proposition is the cornerstone of logical reasoning. It's a declarative statement that possesses a truth value—meaning it must be either true or false, even if we don't currently know which. It is the core meaning or content of a statement.
This distinguishes propositions from other types of sentences:
- Questions: "Is the sun shining?" (Asks for information, isn't true or false)
- Commands: "Put the book on the table." (Gives an order, isn't true or false)
- Exclamations: "Wow, a supernova!" (Expresses emotion, isn't true or false)
The Fundamental Test:
Ask yourself: "Could this statement, in principle, be proven true or false?" If yes, it's a proposition.
Practice: Identifying Propositions
Test your understanding. Which of the following express a proposition?
1. "Socrates was a human."
2. "Know thyself!"
3. "Nobody knows her true character."
2. Constructing Arguments
An argument in logic is not a dispute. It is a structured set of propositions where one or more statements (the premises) are offered as reasons to believe another statement (the conclusion).
Logic vs. Rhetoric
Arguments can be used for different purposes. Rhetoric is the art of persuasion, using arguments to "win" a debate or convince an audience, sometimes appealing to emotion. In contrast, philosophy uses arguments as a tool for learning and discovering truth. Our focus here is on the logical structure of arguments, not their persuasive power.
Premises and Conclusions
The role a proposition plays depends on the context. A statement can be a conclusion in one argument and a premise in another.
Example: Shifting Roles
Argument A:
1. All humans are mortal.
2. Socrates is human.
∴ 3. Therefore, Socrates is mortal.
Argument B:
1. Socrates is mortal. (Now a premise)
2. All mortals have finite lifespans.
∴ 3. Therefore, Socrates has a finite lifespan.
3. Spotting Arguments: Indicator Words
English provides helpful clues for identifying premises and conclusions. While not always present, these indicator words are strong signals of an argument's structure.
Premise Indicators
- since
- because
- for
- as
- given that
- seeing that
- for the reason that
- inasmuch as
- owing to
- if...
Conclusion Indicators
- therefore
- thus
- hence
- so
- consequently
- it follows that
- we may conclude
- as a result
- which means that
- ...then
4. Advanced Analysis
Real-world arguments are rarely as neat as our examples. They often contain unstated assumptions, multiple steps, and persuasive language that isn't part of the core logic.
Enthymemes: The Unstated Premise
An enthymeme is an argument with a missing or unstated premise. The speaker assumes the audience will fill in the blank. To properly evaluate the argument, we must make this hidden premise explicit.
Example: Celebrity Endorsement
"Jennifer Aniston's new skincare line has sold out everywhere. You should try it."
Stated Premise: Jennifer Aniston's skincare line is very popular.
Conclusion: You should try it.
Unstated Premise: You should try products that are popular and endorsed by celebrities known for their appearance.
By stating the hidden premise, we can see the argument relies on an appeal to popularity and authority, which we can then evaluate.
Chain Arguments & Subordinate Conclusions
In a complex argument, the conclusion of one step can become a premise for the next. This creates a chain of reasoning. The intermediate conclusions are called subordinate conclusions.
Example: Chain of Consequences
"Watch your thoughts, for they become words. Watch your words, for they become actions. Therefore, watch your thoughts, for they become your actions."
Premise 1: Your thoughts become words.
Subordinate Conclusion 1 / Premise 2: Your words become actions.
Main Conclusion: Your thoughts become your actions.
Case Study: Socrates on Trial
In Plato's Apology, a condemned Socrates argues that death may be a blessing. This is a complex argument with multiple lines of reasoning, unstated premises, and rhetorical flourishes. Let's dissect the core logic.
"...there is great reason to hope that death is a good, for one of two things: - either death is a state of nothingness and utter unconsciousness, or, as men say, there is a change and migration of the soul from this world to another. Now if you suppose that there is no consciousness... death will be an unspeakable gain... But if death is the journey to another place... what good, O my friends and judges, can be greater than this?"
Logical Breakdown:
- Premise 1 (Dilemma): Either death is (A) a state of nothingness, or (B) a migration of the soul.
- Premise 2 (Conditional): If death is (A) a state of nothingness, it is like a dreamless sleep, which is a gain.
- Premise 3 (Conditional): If death is (B) a migration of the soul to a better place, it is a great good.
- Main Conclusion: Therefore, death is a good (a blessing).
Notice how rhetorical parts like "O my friends and judges" are not part of the logical structure. The skill is to separate this "rhetorical chaff" from the "argumentative corn."
5. Test Your Skills: Practice Arguments
Apply what you've learned. For each example, identify the premises (stated and unstated) and the conclusion.
1. "If universal basic income is so good for the economy, no one should complain that it's funded by taxes." What is the implied conclusion of someone making this argument critically?
2. "Smartwatches are more hassle than they are worth. You have to charge them daily, and on the rare occasion you use an advanced feature, you'd rather just use your phone." What is the main conclusion?
3. "The soul is immortal, so there's no such thing as a dead soul." What is the unstated premise required for this argument to work?
4. "It doesn't matter who you vote for, because the government always gets in." What is the premise of this argument?