Day 2 / Chapter 2
Knowing how to construct and evaluate definitions is vital to critical thinking:
1. If we are trying to decide whether to accept or believe some claim, then we need to
make sure that we understand the claim
2. Mastering an academic discipline requires understanding its key concepts
3. Solving problems requires knowing how to define the problem and potential solutions
We’ll study a definition method that can help
Let’s start with some basic facts about language
AS we saw, knowledge is justified true belief. To claim that something is true is to assert it
o Asserting is not the same supposing, considering, assuming, pretending that, etc.
o To assert is to say that something is a fact or is true
o We use complete sentences to assert something
o Let’s call what we assert using a complete sentence a proposition
o Not every complete sentence can be used to make an assertion.
o Example: Sentences can be used to ask questions or express support, they are not
used to say that something is true or false. So they are not used to assert something
o Different sentences can be used to assert the same proposition
o EX: John is a Liar. John is Mendacious
o These are two ways of saying the same thing.
o A given sentence can be used to assert more than one proposition
o Bill’s wife is mad at him
o Asserts that Bill has a wife
o Asserts that she is angry
o Asserts that she is angry at him
The Assertion Test To tell whether some proposition is asserted in a sentence, ask whether the sentence as a
whole could be true even if that proposition were false
If the sentence is TRUE when the propositions are FALSE, then that proposition is not
If the sentence is FALSE when the propositions are FALSE, then that proposition is
A conjunction is a sentence with an “and” in it. Let’s call the two parts, “conjuncts”. How any
proposition does that sentence assert?
Yonge is Busy and Dundas is long. Two assertions, Yonge is busy. Dundas is long
o A conjunct is true only when both of its conjuncts are true
o That is, if one of theme is false, then the entire conjunction is false too
o A disjunction is a sentence with an “or” in it
o A disjunction does not assert either disjuncts, example:
o Either John is Late or my clock is fast
o One is not asserting that John is Late, and one is not asserting that the clock is fast
o Rather, one is asserting that one, or both, of the disjuncts is true, even if we do not
A conditional statement is a statement with an “if” in it. If P, then Q.
The antecedent – what follows the word “if”
The consequent – what follows the word “then”
A conditional does not assert the antecedent or the consequent. “If David Hunter is PM, then he
is a politician”.
That is true, even though neither the antecedent nor the consequent is true. It asserts that a
relation holds between the antecedent and the consequent: that the truth of the antecedent is
sufficient for the truth of the consequent.
Asserts a much more complicated idea that if the antecedent where true, the consequent
would be true too. Each separate part is false, however together they form a truth
Noun Clauses – CHECK IN TEXTBOOK 3 TYPES A noun clause is a complete sentence prefixed with a “that”. The following contain noun clauses
1. John said that oysters are delicious
2. Peter believes that oysters are delicious
3. Simon knows that oysters and delicious
THESE ARE 3 TYPES