Privity of Estate

One of the concepts in our Property class which seems to confuse people is called privity of estate. Essentially, two parties have privity of estate when they can trace their land back to a common parcel. However, the analysis taught in our casebook and in the literature (I think even going back before Llewellyn) uses a two part process: first look for "vertical privity" on each side, back in time to a party who has "horizontal privity" with a common vendor.

Well, there's no reason why the terms "horizontal" and "vertical" make any sense in this context. Our casebook authors suggest that professors have, from time immemorial, drawn the analysis on a chalk board, and have put the original vendor and vendees in a horizontal line, and then drew subsequent conveyances in a vertical line (in some imperfect fashion representing time). I think people get confused because the adjectives "horizontal" and "vertical" have no other specialized meaning in this area of law.

As long as we're making terms up, I'd like to suggest some more descriptive phrases for what's occurring in these transactions. Perhaps the term "horizontal privity" would be better described as privity of estate following partition, privity of covenant (if there is an enforceable covenant), shortened to perhaps "partition privity" or "covenant privity" (a related concept is "contract privity"). A vendor who partitions their parcel and sells part of it to a vendee is in "covenant privity" (or "horizontal privity") with the buyer. Then you could have privity of estate in the whole or privity of assignment, which might contract to "transfer privity", "conveyance privity", "whole privity", "assignment privity", or something similar. This describes "vertical privity" in which the vendor conveys an entire parcel (without partition) to a vendee.

Any takers? Does these make more sense than "horizontal" and "vertical" privity?