妙法蓮華經玄贊 7.128

7.128

贊曰：此橫滋也。三乘性異，破乘同病，根性有三，故分三種。《涅槃經》云：「譬如病人有其三種，一若遇良醫及以不遇，決定可差」，即此大草。「二若遇即差，不遇不差」，即此中草。「三若遇不遇定不可差」，即此小草。此三乘中各有稟教、理、行、果四而生長者，故皆說有根莖枝葉。依教證理、依理起行、依行得果，如根莖等生次第故。又依勝劣果、行、理、教如次配之。又解此三之中皆有四法：一種性，二發心，三修行，四得果。此四通三，如次配之，橫名三乘、竪名四類，類依性有故說為橫。亦有說四，即是勝解、見、脩、無學，此義不遍，小草中有，故不取之。

The Commentary says: This is the horizontal moistening. The natures of the three vehicles differ, countering the flaw of taking the vehicles as identical; since their faculties and natures are threefold, they are divided into three kinds.
The *Nirvāṇa-sūtra* states: 'For example, sick people are of three kinds: 1. Whether they meet a good physician or do not meet one, they will definitely recover'—this is the large grass. '2. If they meet one, they recover; if they do not meet one, they do not recover'—this is the medium grass. '3. Whether they meet one or do not meet one, they will definitely not recover'—this is the small grass.
Among these three vehicles, each receives the four [factors] of teaching, principle, practice, and fruit and thereby grows; thus all are said to have roots, stems, branches, and leaves. Relying on the teaching one realizes the principle, relying on the principle one gives rise to practice, and relying on practice one attains the fruit, just as roots, stems, and so forth arise in succession. Furthermore, according to superiority and inferiority, fruit, practice, principle, and teaching are correlated in that order.
Another explanation is that within each of these three there are four dharmas: 1. lineage, 2. generating the aspiration [for awakening], 3. practice, 4. attainment of the fruit. These four apply throughout the three, correlated in that order: horizontally they are called the three vehicles; vertically they are called four classes. Classes exist based on nature; hence they are described horizontally.
There are also those who explain the four as resolute faith, seeing, cultivation, and no-further-learning; but this meaning is not universal—it is found only within the small grass, and therefore is not adopted.