A conditional sentence is a hypothetical (GGBB p. 689). Greek has first, second, and third class conditions.
- A first class condition uses ει in the protasis.
- A second class condition also uses ει but has αν in the apodosis.
- A third class condition uses εαν in the protasis.
A first class condition assumes the truth of the protasis.
A second class condition assumes the protasis to be false.
A third class condition isn’t sure about the protasis.