Chapter 3, Tutorial 5
Fallacies of Presumption

A different sort of fallacy occurs when the arguer tries to slip a fast one by you – a fast one in the way of premises. The argument attempts to trick by hidden or problematic presumption.

For example,

































2. Suppressed evidence–leaving out the important part

Example: So, you need to convince a friend to attend DSU with you. You tell her about the great times, the easy grading policies, and the camaraderie the two of you would share. But you conveniently forget to mention the huge cost of tuition and housing.

You've suppressed some of the most relevant information. The conclusion, that she should attend with you, is vastly undermined by the missing information. So, your attempt to convince is a kind of trickery even if what you say is all true: it's deception by omission.

Remember, inductive reasoning is wholistic. Leaving something known and relevant out of the presumtions destroys the cogency of the argument.


OK, consider this one:



















Halpin says: By definition God has all perfections. So, because existence is a perfection, God must exist! You say: Halpin you're wrong! Steven Pinker has shown that belief in God is just an evolutionary hangover from the need to socialize and show obedience to an Earthly lord.

How should we understand this exchange?
  1. The response to Halpin commits the straw man fallacy.
  2. The response to Halpin commits the red herring fallacy.
  3. Halpin commits the fallacy of begging the question--to define God as perfect is to presuppose that he/she exists.