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# Set-based reasoning

Disciplines Argument > Types of reasoning > Set-based reasoning

## Description

Set-based reasoning is founded on Set Theory. Its arguments range around whether things are members of named groups or not, thus 'A dog is an animal but not a vegetable'.

The basic assumption is one of membership, that an item can be categorized into a given group or set. This also assumes that both the item and the set exist in the first place. The following argument then may include consideration of the overlap between sets and the implications of this.

Set reasoning often thus includes statements along the lines of:

• A is a B

• If A is a B then...

• A is not a B, but it is a C

• A is both C and D, therefore...

## Example

 Say this Not this He works for Microsoft. Microsoft people are intelligent. Therefore he is intelligent. He works for Microsoft and is intelligent. If this is an international standard CD then it will use ISO standard encryption coding. ISO encryption will be used here. If he is both Italian and lives in New York, then he is likely to be fond of pizza. He probably likes pizza.

## Discussion

Set theory makes careful distinction about what a thing is and what it is not. It is thus very precise about definitions and puts a lot of focus here. It also is concerned with membership relationships and hierarchies, seeking higher and lower members of an order.

The verb 'to be' is important here. When we say an item 'is' a member of a set, we assume it has all the attributes of the set. A common error set-based is when we say to a person something like 'you are silly'. The person (or others) may take this description to indicate that they are nothing but silly, having all the attributes of silliness. This can cause significant psychological effects.

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