1. Si haec negotia confecerimus, ad convivium ire poterimus.

Translation: If we finish (will have finished), we will be able to go to the 'party'.

confecerimus: mood-indicative; tense-fut. perf.; reason-statement of fact

2. Nisi illud opus conficias, ad convivium ire non possis.

Translation: Unless you finish that work, you may not be able to go to the 'party'.

possis: mood-subjective; tense-present; reason-imaginzing condition referring to future time

3. Si saxa, et non dentes, lasoni data essent, draco laetior fuisset.

Translation: If rocks not teeth had been given to Jason, the dragon would be happier.

data essent: passive mood, pluperfect tense, contrary to fact