Although [the Essenes] reject oaths, they swear an oath upon entering the community! Moreover, they are allowed to take an oath in a judicial court... what to us may be a contradiction might not have been so for first-century Jews...(Tan Kim Huat, The Zion Traditions and the Aims of Jesus, p.85, n.21)
Interesting? Though it is common sense that the logical law of non-contradiction applies very explicitly in many matters to everyone, yet this law has qualification nonetheless.
Many accuse the canonical gospels for having 'contradictions'. But this might not be so to their first readers.