Most modern heresy has roots in the big five from that period. Just about all the ways you can deviate from Christian orthodoxy were explored as the gospel moved from culture to culture in the ancient world. Before that time—the era of Augustine and Ambrose, Jerome and John Chrysostom and more—the church's theology was argued but not much codified. The canon of Scripture itself was only loosely uniform from place to place. Once the Council of Nicaea (famous for the Nicene Creed) began to nail down what is and is not Christian teaching in 325, any novel thinkers had to pass muster or be excommunicated:officially declared not in communion with the church.

Heresy had its territorial hotbeds. In the Eastern church, most heresy involved the Trinity; in the West, the nature of sin was a wider concern. Eastern heresies gathered like moths to the flame with alternative understandings of Jesus. They included Arianism, Nestorianism, and Monophysitism. Arius was an Egyptian priest who believed Jesus was the son of God, but not an eternal being like God. He viewed Jesus as a creature like the rest of us, therefore denying his divinity. Arianism was answered by the orthodox teaching that Jesus is "begotten, not made, one in being (consubstantial) with the Father." A council in Constantinople fifty years later declared the Holy Spirit also one with the Father and the Son.

Nestorius, a bishop of Constantinople, proposed that Jesus had two distinct persons within: one human, one divine. This idea threatened to make the humanity of Jesus a mirage over his more real, divine nature—essentially pronouncing the Incarnation, Crucifixion, and Resurrection a charade. Nestorianism was condemned by the third council in Ephesus in 431.

The next heresy proceeded from the last one: Jesus had two natures before his birth and afterwards had one (monophysis). The Monophysites had a lot of support in the Near East and some sects exists today. Meanwhile in the West, Augustine began as an adherent in the Manichaean movement, which saw good and evil spirits in an equal pitched battle for control of the world. That God could have an "evil twin" in the devil was contrary to the teaching of One Supreme Being. Manichaeism was condemned, with no small help from Augustine.

Pelagius in Rome was the last big heretic of the period. He taught that human beings could save themselves by spiritual and moral perfection alone—which contradicts the need for God's grace. A lot of Catholics unconsciously harbor the spirit of Pelagianism today.

Scripture: Genesis 1:1-3; Exodus 1-6; Isaiah 45:5-7; John 1:1-18; 3:16-21; 14:15-31; Books: I Believe in God: A Reflection on the Apostles' Creed by Thomas Rausch, SJ  (Liturgical Press, 2008); Beginning to Read the Fathers by James Boniface Ramsey (Paulist Press, 2012)

Suicide is the deliberating taking of one's own life. It may sound simple to pass moral judgment here, but many factors influence the moral value of the decision according to Catholic teaching. For example, a person who witnesses to faith under threat of death is choosing, not death, but the testimony of faith—though death is the sure result. In the same way, medical personnel fighting highly infectious diseases may hear from their relatives that entering such a medical arena is "suicide"—yet the choice is clearly not to die, but to serve.

 Modern health care offers extensive means of maintaining biological life. To refuse ordinary care is considered suicide in church teaching, but to refuse extraordinary means of care is not. These distinctions may seem unclear to the layperson but consultations with doctors and chaplains will help clarify the categories. To refuse extraordinary treatments allows the pathology of a disease to run its course, not to actively terminate a life. My sister, for example, was pronounced terminally ill but told that radiation treatments would extend her life for a few months. She tolerated treatment poorly, however, and chose palliative care (for the alleviation of pain only) for the last months of her life instead.

In our times, euthanasia (mercy killing) and assisted suicide have gained many advocates.  Euthanasia is a decision made on behalf of the sick person by a third party, as when someone is comatose or mentally incapable of rational choice. Assisted suicide, sometimes called aid-in-dying, involves a deliberate choice to end one's life with medical assistance. Popular arguments in favor of assisted suicide are the principles of autonomy and utility. Autonomy argues that human beings have a right to freely choose their path. It presumes that a person is free to make the decision to die unimpeded by coercion, stress, crisis, or narcotic substances. Utility argues that an individual's death might be best for all concerned due to economic factors or the burden placed on caregivers.

Catholic teaching on suicide does not accept arguments from autonomy or utility. Our moral tradition is based on four positive principles: the sanctity of human life, the sovereignty of God, personal stewardship, and the commandment against killing. Still, pastoral practice no longer passes judgment on the suicide, as most such acts are not fully voluntary but rather entered under duress. Christian burial is therefore available for the victim of suicide.

Scriptures: Exodus 20:13; Deuteronomy 30:19-20; 1 Samuel 2:1-10; Job 1:21; Isaiah 45:4-25. Books: Suicide, Despair, and Soul Recovery  by Ken Stifler (Mahwah, NJ: Paulist Press, 2008); Moral Discernment, Moral Decisions Guide by Richard Gula, SS (Mahwah, NJ: Paulist Press, 1997).