In historical-critical analysis, the L source is an hypothetical oral tradition which Luke may have used when composing his gospel. It includes the virgin birth of Jesus and many of Jesus' best loved parables. Like Matthew's unique source, known as M, the L source has important parables. Two which appear in L are the Good Samaritan and the Prodigal Son. I. Howard Marshall states "Luke rightly regarded these sources as reliable".
According to the four-document hypothesis, Luke combined Mark, the Q source, and L to produce his gospel. The material in L, like that in M, probably comes from the oral tradition. Luke's special material composes nearly half of his gospel.
The question of how to explain the similarities among the Gospels Matthew, Mark, and Luke is known as the synoptic problem. The hypothetical L source fits a contemporary solution in which Mark was the first gospel and Q was a written source for both Matthew and Luke.
- Funk, Robert Walter; Hoover, Roy W.; Jesus Seminar (1993). "Introduction". The Five Gospels: The Search for the Authentic Words of Jesus. New Translation and Commentary. HarperSanFrancisco. pp. 1–30. ISBN 978-0-02-541949-0.
- Jones, Brice (2011). Matthean and Lukan Special Material: A Brief Introduction with Texts in Greek and English. Wipf and Stock Publishers. ISBN 978-1-61097-737-1.
- Marshall, I. Howard (1994). "LUKE. Introduction". In Carson, D. A.; et al. (eds.). New Bible Commentary: 21st Century Edition. Inter-Varsity Press. p. 979. ISBN 978-0-85110-648-9.
- Theissen, Gerd; Merz, Annette (1998). "Chapter 2. Christian sources about Jesus.". The Historical Jesus: A Comprehensive Guide. Translated from German (1996 edition). Fortress Press. ISBN 978-0-8006-3123-9.
- Edwards, James (2009). The Hebrew Gospel and the development of the synoptic tradition. Grand Rapids, Michigan: Eerdmans. ISBN 0-8028-6234-9. OCLC 368048433.
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- Kloppenborg, John S. (2011-04-14). "The Hebrew Gospel and the Development of the Synoptic Tradition (review)". Toronto Journal of Theology. 27 (1): 109–111. doi:10.1353/tjt.2011.0000. ISSN 1918-6371.