In informal logic

Informal logic

Informal logic, intuitively, refers to the principles of logic and logical thought outside of a formal setting. However, perhaps because of the informal in the title, the precise definition of informal logic is matters of some dispute. Ralph H. Johnson and J...

, an inference objection

Objection (argument)

In informal logic an objection , is a reason arguing against a premise, lemma or main contention. An objection to an objection is known as a rebuttal.-See also:* Argumentation theory* Argument map...

is an objection to an argument based not on any of its stated premises, but rather on the relationship between premise

Premise

Premise can refer to:* Premise, a claim that is a reason for, or an objection against, some other claim as part of an argument...

 and contention. For a given simple argument, if the assumption is made that its premises are correct, fault may be found in the progression from these to the conclusion of the argument. This can often take the form of an unstated co-premise

Co-premise

A co-premise is a premise in reasoning and informal logic which is not the main supporting reason for a contention or a lemma, but is logically necessary to ensure the validity of an argument...

, as in Begging the question

Begging the question

Begging the question is a type of logical fallacy in which the proposition to be proven is assumed implicitly or explicitly in the premise....

. In other words, it may be necessary to make an assumption in order to conclude anything from a set of true statements. This assumption must also be true in order that the conclusion follow logically from the initial statements.

Example

In the example to the left, the objector can't find anything contentious in the stated premises of the argument supporting the conclusion that "There is no danger in NASA's Stardust Mission bringing material from the Wild 2 comet back to Earth", but still disagrees with the conclusion. The objection is therefore placed beside the main premise and exactly corresponds to an unstated or 'hidden'co-premise. This is demonstrated by the argument map to the right in which the full pattern of reasoning relating to the contention is set out.