Ula says that a Rasha Arum is a person who learned Mikra and Mishnah but he did not learn from a Talmid Chacham. (1)
Rebbi Eliezer says that a person who learned Mikra and Mishnah but did not learn from a Talmid Chacham is an Am ha'Aretz. (2)
Rebbi Meir says that an Am ha'Aretz is someone who does not recite Keri'as Shema with the Berachos. (3)
The Chachamim say that one who does not wear Tefilin is an Am ha'Aretz, but Ben Azai says that it is a person without Tzitzis on his clothing. (4)
Someone who learns Mikra without Mishnah is a Bor (worse than an Am ha'Aretz).
Rebbi Huna says that when someone does an Aveirah twice he regards it as something permissible.
Rebbi Yochanan said that he learned fear of sin from a Besulah who prayed that she will not be the cause of people to sin.
Rebbi Yochanan said that he learned how to receive extra reward from a widow who went to a distant Shul in order to receive extra reward.
Those that decide Halachah in accordance with the Mishnah are destroyers of the world.
A Talmid who decides Halachah before he is ready destroys the world.
A Talmid Chacham who is ready to decide Halachah but fails to do so also causes destruction.
A Talmid Chacham is not ready to decide Halachah until he is 40 years old. (5)
There are seven types of Perushim (people that fraudulently act as if they are big Tzadikim).
A person should learn Torah she'Lo Lishmah because as a result of learning she'Lo Lishmah a person will eventually learn Lishmah.
The Heavenly Beis Din will punish those that fraudulently pretend to be Perushim.
Rebbi Shimon says that a merit does not save a Sotah.
Rebbi says that a merit does save a Sotah, but she will not give birth and she will weaken and eventually die the death of a Sotah.
A BIT MORE
1. Since he did not learn from a Talmid Chacham he does not understand the Mishnah properly and his Halachic decisions will inevitably be erroneous. He is an Arum because people who see him learning Mishnah will assume he is a Talmid Chacham and will honor him as a Talmid Chacham.
2. Rebbi Shmuel Bar Nachmani says that he is a Bor, Rebbi Yanai says that he is a Kusi and Rebbi Acha Bar Yakov says that he is a Magush (sorcerer).
3. An Am ha'Aretz is not trusted regarding Taharos and Ma'asros and his Maga is regarded as Tamei.
4. Rebbi Yonasan Bar Yosef says that an Am ha'Aretz is someone who has children and does not raise them to learn Torah. Acherim say that an Am ha'Aretz is someone who learned Mikra and Mishnah but did not learn from a Talmid Chacham.
5. If the Talmid Chacham is equal to the Gadol of the city or if there is no one else older than him he may decide Halachah under the age of 40.
WORSE THAN AN AM HA'ARETZ
Rashi says that a Bor is worse than an Am ha'Aretz. The Maharsha explains that a Bor lacks basic Midos and Derech Eretz while an Am ha'Aretz lacks wisdom and Torah but he does have basic Derech Eretz. A Kusi is worse even than a Bor because a Kusi is not concerned with the dictates of the Chachamim and therefore does not perform the Mitzvos properly.
PREMATURELY DECIDING HALACHAH
A Talmid Chacham who is not ready to decide Halachah but does so anyway is a Rasha, a Shoteh and conceited. A Talmid Chacham who is ready to decide Halachah but fails to do so withholds Torah and places stumbling blocks in front of the blind. The small Talmidim who have not learned sufficient Torah and wish to act self-important in front of the Amei ha'Aretz and their townspeople and they jump to sit at the head for Dinim and Halachic decisions are the cause for increased disputes in Klal Yisrael and they destroy the world and extinguish the flame of Torah and damage the vineyard of Hashem Tzvakos. (Rambam Hilchos Talmud Torah 5:4)