Simple example of necessity logic
B: Ensure a sufficient amount of heat
D: Buy a lighter
A: Start a campfire
Click on the icons on the arrows to see assumptions and injections
C: Have fuel
D': Buy wood
In order to Start a campfire I must Ensure a sufficient amount of heat and in order to Ensure a sufficient amount of heat I must Buy a lighter. But, in order to Start a campfire I must also Have fuel and in order to Have fuel I must Buy wood. I can't both Buy a lighter and Buy wood.
|D-D'||1. I don't have money to buy both.|
2. I don't already have either wood or a lighter lying around.
3. I can't borrow money.
|B-D||1. I don't have matches.|
2. I don't have a magnifying glass and/or the sun isn't shining.
3. I can't borrow a lighter/matches from someone.
|C-D'||1. I have nothing I can use as a fuel-source.|
2. I can't get wood for free anywhere.
|A-B||1. Heat is necessary to start a fire|
|A-C||1. Fuel is necessary to start a fire|