Three types of logic

In this article we discuss three different modes of reasoning. Two of them are very common, but the third is not and is essential to delivering new ideas.

Deductive logic

This is a simple system that guarantees a logical output if the inputs are logical. In other words “if the rules are true, then this is true”.

For example:

• All even numbers are divisible by 2

• 42 is an even number

• Therefore 42 is divisible by 2

• If the sign is in the window the shop is open

• The sign is not in the window

• Therefore the shop is not open

We took accurate input statements and deduced a logical output statement.

Inductive logic

In this system you take a series of observations and try to find a rule that is very likely to be true in all situations (but not guaranteed like deductive reasoning). In other words “X keeps happening, it is probably a rule”.

For example:

• When it is sunny in the morning, the birds sing

• Therefore rule = good weather in the morning means the birds will sing

• Aluminium expands when hot

• Copper expands when hot

• Steel expands when it is hot

• Therefore rule = all metal expands when hot

Abductive logic

Here we are not looking for a rule that we can apply everywhere, but instead we are looking for a best explanation of what we have observed - “X has happened, the best explanation is Y”.

For example:

• The phone won’t turn on

• Therefore an explanation is that the battery is depleted (can be tested)

• Users have stopped purchasing this product

• Therefore an explanation is the product is too old fashioned (can be tested)

This type of thinking leads to testable hypothesises than can lead to new information. There might be lots of explanations for an event, and this leads to interesting new lines of work.

Summary

Looking at complex problems with abductive logic gives you permission to explore new hypothesis and uncover new insights as you are not bogged down by trying to find a hard truth immediately - but open yourself up to discovery.