In the complex hierarchy of English feudalism, seisin represented more than mere occupancy; it was the formal investiture of land which established a tenant's right to hold a freehold. Unlike modern ownership, seisin was rooted in the concept of 'livery of seisin,' a public ritual where the transferor handed a clod of earth or a twig to the transferee in the presence of witnesses. This physical act symbolized the conveyance of the 'corporeal hereditament' and was essential because, historically, the law prioritized the visible, public manifestation of landholding over private written instruments. It was the crucial link between the land itself and the rights of the nobility to exercise jurisdiction and collect rents.
From a heraldic and genealogical perspective, seisin was the cornerstone of inheritance. A 'seisin in deed' occurred when a person actually entered the lands, whereas 'seisin in law' existed when an heir had the right to enter but had not yet physically done so. Under the principle of 'Seisina facit stipitem' (seisin makes the stock), the actual possession of the land by an ancestor determined the line of descent for future claimants. This rendered the timing and legality of seisin a frequent point of contention in high court battles over peerages and ancestral seats, as the loss of seisin often meant the loss of both wealth and noble status.