Please explain each ground on why contracts became inexistent and void, these are from the Civil Code of the Philippines Article 1409

a)Those whose cause, object or purpose is contrary to law, morals, good customs, public order, or public policy.

b)Those which are absolutely simulated or fictitious.

c)Those whose cause or object did not exist at the time of the transaction.

d)Those whose object is outside the commerce of men.

e)Those which contemplate an impossible service

f)Those where the intention of the parties relative to the principal object of the contract cannot be ascertained.

Those expressly prohibited or declared void by law.