1. Synoptic Problem: The Synoptic Gospels reveal many similarities in content, structure, and even wording. This phenomenon is often referred to as the "Synoptic Problem." Scholars believe that these similarities indicate some form of literary dependence among these gospels.
2. Two-Source Hypothesis: One explanation for the Synoptic Problem is the Two-Source Hypothesis. This hypothesis suggests that Matthew and Luke primarily used two sources in composing their gospels: the Gospel of Mark (which they both heavily depend on) and a hypothetical collection of sayings and teachings of Jesus, often called the "Q" source.
3. Q Source: The "Q" source, or the "Quelle" (German for "source"), is a term used to refer to a hypothetical sayings gospel or collection of Jesus' teachings that was independently used by Matthew and Luke in addition to Mark. Scholars reconstruct the content of Q based on the common material in Matthew and Luke that cannot be found in Mark.
4. Triple Tradition: The "Triple Tradition" refers to the passages or sayings that are shared by Matthew, Mark, and Luke. These include the account of Jesus' baptism, the parables of the sower, the mustard seed, and the prodigal son, among others. The Triple Tradition provides evidence for a common oral or written tradition that was influential in the development of the Synoptic Gospels.
5. Double Tradition: The "Double Tradition" refers to passages or sayings that are shared by Matthew and Luke, but not found in Mark. These passages include the Sermon on the Mount/Plain, the Beatitudes, the Lord's Prayer, the Parable of the Good Samaritan, and various instructions and parables. The Double Tradition suggests a literary connection between Matthew and Luke beyond their dependence on Mark.
6. Sondergut: The term "Sondergut" (German for "special possession") refers to material that is unique to a particular gospel and is not found in the other two Synoptic Gospels. Matthew, Mark, and Luke each have their own distinctive sections and passages (e.g., the infancy narratives in Matthew and Luke, and the Parable of the Rich Fool in Luke) that are not present in the other gospels.
These literary relationships among the Synoptic Gospels provide insights into the ways in which the early Christian communities transmitted and developed the oral and written traditions about Jesus and his teachings. They also shed light on the process of gospel composition and the theological perspectives and emphases of each evangelist.