[C]onscientia est sicut praeco Dei, et nuntius; et quod dicit, non mandat ex se, sed mandat quasi ex Deo, sicut praeco, cum divulgat edictum regis.  Et hinc est, quod conscienta habet virtutem ligandi in his, quae possunt aliquo modo bene fieri.

“Conscience is like God's herald and messenger; and what it says, it does not command of itself, but commands it as coming from God, like a herald proclaiming the edict of the king.  So it is that conscience has the power to bind us concerning things which can in some way be done well.”

-- St. Bonaventure, II Librum Sententiarum, Distinction 39, Article 1, Question 3, Conclusion