Natural Law

First seen in plays in early greek/roman years
Aristotle also wrote about it being "the natural that is which everywhere is equally valid"

In his book Summa Theologica in 13th century
It is an absolutist theory (actions are always good/evil in every situation)
Deontological (Same thing really)

Aquinas said it was "the moral code existing within the purpose of nature created by God"
Natural law exists to help humans find their destiny with God
All humans were born good because natural law exists within everyone
Noone commits an evil act willingly (according to Aquinas)

One main natural law is "Good is to be persued and evil is to be avoided" 

Aquinas came up with the precepts to help us to find our goal

Primary precepts:
W orship God
O rdered society
R eproduction
L earning (educate the young)
D efend the innocent (self preservation) (protect human life)

Secondary precepts:
Thes come from the primary precepts and are the deontological absolute rules. Such as the ten commandments or our rules of society
For example the precept "Protect the innocent" would become "Do not abort" or "Do not kill" as a secondary precept

Aquinas saw everyone as good 
Noone could persue an evil act knowingly
People act the way they do because they think it is good

He explained this as "real" and "apparent" goods
"Real" goods were actual good actions which brought us closer to god and helped fullfil our destiny
"Apparent" goods are acts which we do in the heat of the moment or we think they will bring good for us but actually they do not fullfil our aims to be one with God

For example: Stealing food to stop from being hungry is an apparent good, because stealing is wrong: it is written in the commandments. A deontologicalist would encourage starving families not to steal but to seek aid such as family, friends, neighbours, shelters and organisations.

Aquinas believed that it was not just the action but the intention which was important
The interior act is the intention
The exterior act is the act itself
If you gave half of your money to charity that is a good exterior act, but if you only did it to look good infront of your community that is a bad interior act.
Aquinas says you should only do something if both the exterior and interior acts are good