Lecture 2 – Scientific inference
Deduction and induction
Deductive inference: all Frenchmen like red wine + peirre is a Frenchman
(premises) = therefore, Pierre likes red wine (conclusion)
Truth-preserving: if the premises are true then the conclusion must be true too
Justification-preserving: if you’re justified in believing premises you’re justified
in believing the conclusion
Inductive inference: the first give eggs in the box were good + all the eggs
have the same best-before date stamped on them = therefore the sixth egg
will be good too
No truth-preserving: the conclusion can be false
Justification-preserving: ? hard to say
We rely on inductive inference during live (when turning on your computer in the
morning you are confident it will not explode in your face. This because it never
happened. But is can explode this time).
Scientist also use inductive inference (people with Down Syndrome have 3 copies of
chromosome 21. So, all people with Down Syndrome have 3 copies of also those
who have no examination on it – scientists’ reason inductively when they move from
limited data to more general conclusion)
Most philosophers think science relies on induction. But Popper claimed that scientist
only need to use deductive. Popper’s argument for this was: although a scientific
theory can never be proved true by a finite amount of data it can be proved false or
refuted AND it was motivated by the belief that Hume had shown the unjustifiability of
induction (see Hume’s problem)
So, if a scientist is trying to refute the theory rather than establish its truth their goal
could be accomplished without the use of induction.
The weakness of Popper’s argument is that the goal of science is not solely to refute
theories but also to determine which theories are true.
So, Popper’s attempt to show that science can get by without induction does not
succeed.
Hume’s problem
Hume argued that the use of induction cannot be justified at all. We use it every day
in life and in science but cannot give a good reason for using it.
Whenever we make inductive inferences we seem to presuppose what he called the
uniformity of nature (assumption that objects we haven’t examined will be similar to
objects of the same sort that we have examined). In each case the reasoning
depends on the assumption that objects we haven’t examined will be similar, in
relevant respects, to objects of the same sort that we have examined. That
assumption is what Hume means by uniformity of nature.
Since a non-uniform world would be logically impossible, it follows that we cannot
prove that the uniformity assumption is true.
Deduction and induction
Deductive inference: all Frenchmen like red wine + peirre is a Frenchman
(premises) = therefore, Pierre likes red wine (conclusion)
Truth-preserving: if the premises are true then the conclusion must be true too
Justification-preserving: if you’re justified in believing premises you’re justified
in believing the conclusion
Inductive inference: the first give eggs in the box were good + all the eggs
have the same best-before date stamped on them = therefore the sixth egg
will be good too
No truth-preserving: the conclusion can be false
Justification-preserving: ? hard to say
We rely on inductive inference during live (when turning on your computer in the
morning you are confident it will not explode in your face. This because it never
happened. But is can explode this time).
Scientist also use inductive inference (people with Down Syndrome have 3 copies of
chromosome 21. So, all people with Down Syndrome have 3 copies of also those
who have no examination on it – scientists’ reason inductively when they move from
limited data to more general conclusion)
Most philosophers think science relies on induction. But Popper claimed that scientist
only need to use deductive. Popper’s argument for this was: although a scientific
theory can never be proved true by a finite amount of data it can be proved false or
refuted AND it was motivated by the belief that Hume had shown the unjustifiability of
induction (see Hume’s problem)
So, if a scientist is trying to refute the theory rather than establish its truth their goal
could be accomplished without the use of induction.
The weakness of Popper’s argument is that the goal of science is not solely to refute
theories but also to determine which theories are true.
So, Popper’s attempt to show that science can get by without induction does not
succeed.
Hume’s problem
Hume argued that the use of induction cannot be justified at all. We use it every day
in life and in science but cannot give a good reason for using it.
Whenever we make inductive inferences we seem to presuppose what he called the
uniformity of nature (assumption that objects we haven’t examined will be similar to
objects of the same sort that we have examined). In each case the reasoning
depends on the assumption that objects we haven’t examined will be similar, in
relevant respects, to objects of the same sort that we have examined. That
assumption is what Hume means by uniformity of nature.
Since a non-uniform world would be logically impossible, it follows that we cannot
prove that the uniformity assumption is true.
