INDUCTIVE AND DEDUCTIVE REASONING
Discerning the structure of an argument is only the first step
in assessing arguments. Students must also learn to critically evaluate
arguments. That means asking whether the premises really do support the
conclusions. It also means asking whether or not the premises themselves are
true. It’s the first part that is the hardest thing for most students. We are
all accustomed (to varying degrees) to questioning the truth of someone’s
claims. What we do not often ask is whether someone’s conclusion really does
follow from his/her premises.
Mastering the art of picking out premises and conclusions is the first step
toward good analytical thinking, but we must also think about whether the
premises really do support their conclusions. Making that sort of determination
requires that we think a little bit about the different kinds of arguments.
There are several ways of categorizing arguments, but for our purposes, we can
distinguish all arguments into one of two types: deductive and inductive.
Deductive argument: an argument whose premises make its conclusion certain
Inductive argument: an argument whose premises make its conclusion likely
(Note: Some dictionaries – and even some older logic texts – define deductive arguments as arguments that reason from the general to the specific and inductive arguments as those that reason from the specific to the general. That particular usage of the terms is obsolete.)
The difference between deductive and inductive arguments is easiest to see by way of examples.
- Smith owns only blue pants and brown pants. Smith is wearing a pair of his pants today. So Smith is wearing either blue or brown pants today.
This is an instance of a deductive argument. We can tell that the argument is deductive because the two premises (that is, the first two sentences) guarantee the truth of the conclusion. If the two premises really are true, then there is no possible way that the conclusion could be false. Here’s another example:
- The soccer game is on either Thursday or Friday. I just found out that the game is not on Thursday, so the game must be on Friday.
Again, this is a deductive argument, for the truth of the premises guarantees the truth of the conclusion. Contrast those examples with this one:
- January has always been cold here in Siberia. Today is January 14th so it is going to be another cold day in Siberia.
This argument is inductive. The premises make the conclusion likely, but they do not guarantee that the conclusion is true.
Now, write your own thesis statement:
What is your TOPIC?
How are you going to discuss it in your essay? (FACT, VALUE or POLICY).
What is the premise of your argument?
What category is your argument in INDUCTIVE or DEDUCTIVE?
Why is this important? (ETHOS, PATHOS, or LOGOS)