Evolution of Halacha
The Written and Oral Torah
The Written Torah
The Written Law is called the Tanach. The Tanach is made up of three sections, Torah Neviim and Ketuvim. The Torah in consists the five books of Moses and was received on Mount Sinai. The Neviim section is the "prophets", some of the names of these prophets are Samuel, Joshua and Jonah. The final section of the Tanach is the Ketuvim which translates to the "writings". The Ketuvim is made up with stories and the megillot such as, Esther and Ruth.
The Written Torah was given by g-d, but there are two different opinions about the Written Torah one orthodox and one reform. Orthodox Jews believe the Torah was written by g-d and since all mitzvot 32 were written by g-d they must be obeyed and are immutable. On the other hand reform Jews believe the written Torah may have only been inspired by g-d, so therefore if g-d didn't write the Torah the mizvot don't need to be obeyed.
The Oral Torah
There are five parts of the Oral Torah. These parts are the Mishna, Gemara, Commentators, Codes and the Responsa.
Mishna: The Mishna covers the discussions and decisions of the rabbis and scholars from 200 BCE to 200 CE. The Mishna is broken up into six sections. The Mishna was edited and written down by Rabbi Yehuda Hanasi at around 200 BCE. The Mishna was written down at this time because at this passage of time for the Jews raised the possibility that the details of the oral traditions would be forgotten.
Gemara: In the three centuries following the compilation of the Mishnah, rabbis throughout Israel and Babylonia analysed, debated and discussed that work. These discussions were recorded in writing, and form the Gemara.
Commentators: The commentaries were intended to help understand the early teachings, Torah and Talmud. Some famous commentators are Rashi and Ramban.
Codes: There is a huge amount of Jewish text and it would be near impossible to know what writing is on, so thats why the idea to codify this material was introduced. To codify means to separate the decisions from the discussions and arguments of rabbis and only record the end result. There are some pros and cons of the codification some pros are it makes Jewish law accessible to the average Jew; allows Jews to know what exactly to do. It also gives a definite answer. Although there are still some cons for the codification such as Jewish law because less flexible and less diversity of opinions. By giving a definate answer there is less chance of discussion and different interpretations. The most famous code of Jewish law are Mishneh Torah written by Rambam and the Shulchan Aruch written by Josef Caro.
Responsa: The Respona is the questions and answers on modern day issues. the responsa was created by rabbis to make Jewish life simpler to answer.