Section — Wouters, Manual of Moral Theology
§ V. On the Extrinsic Form of Contract
843.
I. Notion. By the extrinsic form of a contract are understood the solemnities, according to law, to be employed in entering at least some contracts.
844.
II. Division. 1. The extrinsic form of a contract is divided:
With Canon Law considered, into essential and accidental, according as it is required for validity or only for liceity; thus the presence of witnesses and of the pastor for matrimony is essential; but that matrimony must be entered into publicly pertains to the accidental form.
With civil law considered, some solemnities are sometimes required for merely proving the contract; others are in some way necessary for validity, as we shall explain more fully in the scholion.