In Rajesh Kumar Daria etc. v. Rajasthan Public Service Commission and others (2007) 8 SCC 785, a bench of three judges of Supreme Court considered the difference between vertical and horizontal reservations as under:-
“8. We may also refer to two related aspects before considering the facts of this case. The first is about the description of horizontal reservation. For example, if there are 200 vacancies and 15% is the vertical reservation for SC and 30% is the horizontal reservation for women, the proper description of the number of posts reserved for SC, should be: “For SC: 30 posts, of which 9 posts are for women.” We find that many a time this is wrongly described thus: “For SC: 21 posts for men and 9 posts for women, in all 30 posts.” Obviously, there is, and there can be, no reservation category of “male” or “men”.
9. The second relates to the difference between the nature of vertical reservation and horizontal reservation. Social reservations in favour of SC, ST and OBC under Article 16(4) are “vertical reservations”. Special reservations in favour of physically handicapped, women, etc., under Articles 16(1) or 15(3) are “horizontal reservations”. Where a vertical reservation is made in favour of a Backward Class under Article 16(4), the candidates belonging to such Backward Class, may compete for non-reserved posts and if they are appointed to the non-reserved posts on their own merit, their number will not be counted against the quota reserved for respective Backward Class. Therefore, if the number of SC candidates, who by their own merit, get selected to open competition vacancies, equals or even exceeds the percentage of posts reserved for SC candidates, it cannot be said that the reservation quota for SCs has been filled. The entire reservation quota will be intact and available in addition to those selected under open competition category. (Vide Indra Sawhney, R.K. Sabharwal v. State of Punjab (1995) 2 SCC 745, Union of India v. Virpal Singh Chauhan (1995) 6 SCC 684 and Ritesh R. Sah v. Dr. Y.L. Yamul (1996) 3 SCC 253.)
But the aforesaid principle applicable to vertical (social) reservations will not apply to horizontal (special) reservations. Where a special reservation for women is provided within the social reservation for Scheduled Castes, the proper procedure is first to fill up the quota for Scheduled Castes in order of merit and then find out the number of candidates among them who belong to the special reservation group of “Scheduled Caste women”. If the number of women in such list is equal to or more than the number of special reservation quota, then there is no need for further selection towards the special reservation quota. Only if there is any shortfall, the requisite number of Scheduled Caste women shall have to be taken by deleting the corresponding number of candidates from the bottom of the list relating to Scheduled Castes. To this extent, horizontal (special) reservation differs from vertical (social) reservation. Thus women selected on merit within the vertical reservation quota will be counted against the horizontal reservation for women. Let us illustrate by an example:
If 19 posts are reserved for SCs (of which the quota for women is four), 19 SC candidates shall have to be first listed in accordance with merit, from out of the successful eligible candidates. If such list of 19 candidates contains four SC woman candidates, then there is no need to disturb the list by including any further SC woman candidate. On the other hand, if the list of 19 SC candidates contains only two woman candidates, then the next two SC woman candidates in accordance with merit, will have to be included in the list and corresponding number of candidates from the bottom of such list shall have to be deleted, so as to ensure that the final 19 selected SC candidates contain four woman SC candidates. (But if the list of 19 SC candidates contains more than four woman candidates, selected on own merit, all of them will continue in the list and there is no question of deleting the excess woman candidates on the ground that “SC women” have been selected in excess of the prescribed internal quota of four.)
10. In this case, the number of candidates to be selected under general category (open competition), were 59, out of which 11 were earmarked for women. When the first 59 from among the 261 successful candidates were taken and listed as per merit, it contained 11 woman candidates, which was equal to the quota for “general category women”. There was thus no need for any further selection of woman candidates under the special reservation for women. But what RPSC did was to take only the first 48 candidates in the order of merit (which contained 11 women) and thereafter, fill the next 11 posts under the general category with woman candidates. As a result, we find that among 59 general category candidates in all 22 women have been selected consisting of eleven woman candidates selected on their own merit (candidates at Sl. Nos. 2, 3, 4, 5, 9, 19, 21, 25, 31, 35 and 41 of the selection list) and another eleven (candidates at Sl. Nos. 54, 61, 62, 63, 66, 74, 75, 77, 78, 79 and 80 of the selection list) included under reservation quota for “general category women”. This is clearly impermissible. The process of selections made by RPSC amounts to treating the 20% reservation for women as a vertical reservation, instead of being a horizontal reservation within the vertical reservation.
11. Similarly, we find that in regard to 24 posts for OBC, 19 candidates were selected by RPSC in accordance with merit from among OBC candidates which included three woman candidates. Thereafter, another five women were selected under the category of “OBC women”, instead of adding only two which was the shortfall. Thus there were in all 8 women candidates among the 24 OBC candidates found in the selection list. The proper course was to list 24 OBC candidates as per the merit and then find out number of woman candidates among them, and only fill the shortfall to make up the quota of five for women.”