Non sequitur

(Difference between revisions)
Jump to: navigation, search
m (Construction of a Non-Sequitur)
(Creationist examples: eh... nevermind)
(4 intermediate revisions by 3 users not shown)
Line 1: Line 1:
A non-sequitur (lit. "doesn't follow") is a [[logical fallacy]] in which the premises do not support the conclusion in any way.  Thus, the conclusion doesn't follow from the premises.
+
A '''non sequitur''' (literally, "doesn't follow") is a [[logical fallacy]] in which the [[premise]]s do not support the [[conclusion]] in any way.  Thus, the conclusion doesn't follow from the premises.
  
==Construction of a Non-Sequitur==
+
==Construction of a non sequitur==
  
 
Non sequiturs typically take the following forms:
 
Non sequiturs typically take the following forms:
  
# If A is true, B is true.
+
# [[If]] A is true, B is true.
 
# B is stated to be true.
 
# B is stated to be true.
 
# Therefore, A is true.
 
# Therefore, A is true.
  
A problem with the logical structure of this non sequitur is that it assumes a conditional statement's ("If A, then B") converse ("If B, then A"; See http://www2.edc.org/makingmath/mathtools/conditional/conditional.asp for a more in depth description of this) is always true.  But this is only the case for definitions, where the conditional statement is true.  Furthermore, even if the both premises and the conclusion ''are'' true, the argument is still logically bad since the premises don't support the conclusion.  For example:
+
A problem with the logical structure of this non sequitur is that it assumes a [[conditional]] statement's [[converse]] is always true ("If A, then B" does not imply "If B, then A").  But this is only the case for [[definition]]s, where the given statement is actually a [[biconditional]].  Furthermore, even if the both premises and the conclusion ''are'' true, the argument is still [[invalid|logically bad]] since the premises don't support the conclusion.  For example:
  
 
# If I am human, then I'm a mammal.
 
# If I am human, then I'm a mammal.
Line 23: Line 23:
 
# Therefore, B is not true.
 
# Therefore, B is not true.
  
A problem with the logical structure of this non sequitur is that it assumes a conditional statement's inverse ("If not A, then not B") of a conditional statement is always true.
+
A problem with the logical structure of this non sequitur is that it assumes a [[conditional]] statement's [[inverse]] ("If not A, then not B") of a conditional statement is always true.
  
 
Here's an example:
 
Here's an example:
Line 33: Line 33:
 
Again, the premises don't support the conclusion.
 
Again, the premises don't support the conclusion.
  
It's worth noting that if either of the above examples had said "If and only if A is true, then B is true" as their first premise, they would've been valid and non-fallacious but still unsound.
+
It's worth noting that if either of the above examples had said "[[If and only if]] A is true, then B is true" as their first premise, they would have been valid and non-fallacious but still [[unsound]].
  
 
The above examples are the two main types of non sequitur, however there are many other less common types.  An everyday example would be "If I wear my new shirt, all the girls will think I'm sexy."  However, not all girls will think that the same shirt looks sexy so there really isn't a connection between the two.  This type of non sequitur is commonly seen in advertising.
 
The above examples are the two main types of non sequitur, however there are many other less common types.  An everyday example would be "If I wear my new shirt, all the girls will think I'm sexy."  However, not all girls will think that the same shirt looks sexy so there really isn't a connection between the two.  This type of non sequitur is commonly seen in advertising.
Line 39: Line 39:
 
The two main premises above are good representations of the difference between [[validity vs. soundness|validity and soundness]].
 
The two main premises above are good representations of the difference between [[validity vs. soundness|validity and soundness]].
  
==Creationist Examples==
+
==Creationist examples==
  
A good example of a non-sequitur commonly used by Creationists is the following:
+
A good example of a non sequitur commonly used by [[creationist]]s is the following:
  
 
# No one knows what caused the [[Big Bang]].
 
# No one knows what caused the [[Big Bang]].
# God must've done it.
+
# God must have done it.
  
Obviously the premise doesn't support the conclusion.  In order for this argument to be used the Creationist must first show that the universe couldn't've always existed/come from another collapsed universe/etc, then they must show that science will never solve the problem of the cause of the Big Bang, then they must show that no other god or goddess ever worshipped in human history caused it, then they must prove that the Christian god exists, and finally they must prove that he caused the Big Bang.  Of course, no Creationist would ever take on such a prodigiously difficult task.
+
Obviously the premise doesn't support the conclusion.  In order for this argument to be used the creationist must first show that the [[universe]] couldn't have always existed, come from another collapsed universe, etc.; then they must show that [[science]] will never solve the problem of the cause of the Big Bang,<!-- hmm... really necessary? --> then they must show that no other [[god]] or [[goddess]] ever [[worship]]ped in human history caused it, then they must prove that the [[Christian]] god exists, and finally they must prove that he [[cause]]d the Big Bang.  Of course, no creationist would ever take on such a prodigiously difficult task.
  
 
[[Category:Logical fallacies]]
 
[[Category:Logical fallacies]]

Revision as of 04:00, 12 December 2009

A non sequitur (literally, "doesn't follow") is a logical fallacy in which the premises do not support the conclusion in any way. Thus, the conclusion doesn't follow from the premises.

Construction of a non sequitur

Non sequiturs typically take the following forms:

  1. If A is true, B is true.
  2. B is stated to be true.
  3. Therefore, A is true.

A problem with the logical structure of this non sequitur is that it assumes a conditional statement's converse is always true ("If A, then B" does not imply "If B, then A"). But this is only the case for definitions, where the given statement is actually a biconditional. Furthermore, even if the both premises and the conclusion are true, the argument is still logically bad since the premises don't support the conclusion. For example:

  1. If I am human, then I'm a mammal.
  2. I am a mammal.
  3. Therefore, I'm human.

Even though both the premises and the conclusion are true, the argument is still a fallacy since the premises don't support the conclusion.

Another common non sequitur is this:

  1. If A is true, then B is true.
  2. A is not true.
  3. Therefore, B is not true.

A problem with the logical structure of this non sequitur is that it assumes a conditional statement's inverse ("If not A, then not B") of a conditional statement is always true.

Here's an example:

  1. If I am in my bedroom, then I'm at home.
  2. I'm not in my bedroom.
  3. Therefore, I'm not at home.

Again, the premises don't support the conclusion.

It's worth noting that if either of the above examples had said "If and only if A is true, then B is true" as their first premise, they would have been valid and non-fallacious but still unsound.

The above examples are the two main types of non sequitur, however there are many other less common types. An everyday example would be "If I wear my new shirt, all the girls will think I'm sexy." However, not all girls will think that the same shirt looks sexy so there really isn't a connection between the two. This type of non sequitur is commonly seen in advertising.

The two main premises above are good representations of the difference between validity and soundness.

Creationist examples

A good example of a non sequitur commonly used by creationists is the following:

  1. No one knows what caused the Big Bang.
  2. God must have done it.

Obviously the premise doesn't support the conclusion. In order for this argument to be used the creationist must first show that the universe couldn't have always existed, come from another collapsed universe, etc.; then they must show that science will never solve the problem of the cause of the Big Bang, then they must show that no other god or goddess ever worshipped in human history caused it, then they must prove that the Christian god exists, and finally they must prove that he caused the Big Bang. Of course, no creationist would ever take on such a prodigiously difficult task.

Personal tools
Namespaces
Variants
Actions
wiki navigation
IronChariots.Org
Toolbox