Summarize the following court judgment. Civil Appeals Nos. 11781180/76. Appeals by Special Leave from the Judgment and Order dated 22 9 1976 of the Madras High Court in Writ Petition Nos. 3059/ 75	 W.A. No. 339/76 and W.P. No. 14 respectively. Y.S. Chiale	 V. Subramanyam and Vineet Kumar for the Appellant in C.A. 1178/76. K.S. Ramamurthi	 M.N. Rangachari	 A.R. Ramanathan	 K. Thimmalai	 Jayaraman	 M.M.L. Srivastava and A.T.M.S. Sam path for the Appellant in CAs. 1179 1180/76. V.P. Raman	 Addl. Gen. (In CAs. 1178 to 1180/76	 D.N. Misra	 J.B. Dadachanji for Respondent No. 2 in CAs. 1178 & 1180 of 1976 and Respondent 2 in C.A. 1179/76. K. Parasaran	 Adv. Tamil Nadu	 	A.V. Rangam	 T. Sathiadev and (Miss) A. Subhashini for Respondents in CAs. 1179 80 except Transport Corporation. K. Jayaram	 V.T. Gopalan and K. Ram Kumar for the Appli cant and Intervener in C.A. 1178/76. The Judgment of A.N. Ray C.J.	 and Krishna Iyer	 J. was delivered by Krishna Iyer	 J.M.H. Beg	 J. gave a separate concurring opinion. KRISHNA lYER	 J. A terse presentation of the twin con tentions canvassed before us	 in these appeals by special leave	 after discomfiture at two tiers below	 highlights the importance of the economic role of the State in undertaking	 with legal preferences	 strategic services vital to the community. The keynote thought underlying our decision is that the jural postulates of the old competitive order have to yield place to the new values of developmental jurispru dence. Public law	 in India	 responding to the public needs and the State 's functional role mandated by the Constitu tion	 has evolved new approaches to old problems and given up dogmas which once prevailed during laissez faire days but now have become obsolete because of the 'welfare ' economy which has been nurtured. This radical change in jural 394 perspectives has its impact on canons of statutory construc tion and on verdicts about the vires of legislation. All these generalities acquire appropriate application in the present cases which arise under the (Act IV of 1939) (the Act	 or short) from challenges before the High Court without avail	 by private operators	 of the permit granted to the State Transport Undertaking (STU) by the transport tribunals. The validity of r. 155A of the Motor Vehicles Rules framed under section 68 of the Act is in issue. The core of counsel 's submissions is two fold: (1) Is rule 155A	 assigning five marks for a State undertaking	 not family violative of s 47 of the Act? Does the later amendment to the proviso to section 47 giving preference to State transport systems	 other things being equal	 impliedly repeal	 as contrary to its content	 rule 155A which gives better advantage to the favoured category	 fulfilling the spirit of the statutory amendment more tellingly ? We will proceed further after stating the circumstances leading up to the writ petition before the High Court and the appeal before us. The appellants	 who have come by special leave to this Court	 are private stage carriage operators. We will relate the facts of one case (Civil Appeal No. 1178 of 1976) the decision in which will settle the fate of the rest	 the decisive point of law being identical. The permit of the appellants but on the route Salem to `rode was to have expired on September 13	 1974 and so he applied for renewal under section 58(2) of the Act. The respondent State Transport Undertaking objected to the renewal of the permit urging preferential grounds in its own favour. The State undertak ing 's claim was upheld on the score that it secured higher marks computed with the aid of r. 155 A. Baulked in his application for renewal	 the appellant challenged the order before the Appellate Tribunal. Apprehending an adverse decision on the strength of r. 155 A	 he filed a writ peti tion before the High Court praying that a direction be issued to the Appellate Tribunal to dispose of his appeal without relying on r. 155 A. The plea was negatived by the learned Single Judge and a Division Bench dismissed the appeal therefrom. Aggrieved by the concurrent findings the appellant has assailed before us the vires of r. 155 A as obnoxious to public interest excluding	 in some measure	 a fair competition and being contrary to the proviso to. section 47 (1 ) of the Act. A meaningful discussion of the points debated at the Bar has to begin with a brief outline of the scheme of the in the branch relating to grant of permits for transport vehicles (Chapter IV). All transport vehicles	 before they can be plied in any public place	 require per mits under section 42 and even government vehicles	 if put to commercial use	 have to possess permits. Applications are made for stage carriage permits under section 57 and the consid erations germane to their grant are set out in section 47 of the Act. It is common ground	 and decisions are legion in support thereof	 that the interest of the public generally is the super consideration decisive of the award ' of permits when there is a plurality of applicants. He who can serve the public best gets the permit to ply the stage carriage from the quasi judicial authority charged with the responsi bility for choice. We may read the relevant part of section 47(1) here: 395 (Krishna Iyer	 J.) "47. Procedure of Regional Transport Authority in considering application for stage carriage permit	 (1) A Regional Transport Authority shall	 in considering an application for a stage car riage permit	 have regard to the following matters	 namely : (a) the interest of the public generally; X X X X Provided that other conditions being equal	 an application for a stage carriage permit from any State Transport Undertaking or a Cooperative Society registered or deemed to have been registered under any enactment in force for the time being shall	 as far as may be	 be given preference over applications from individual owners. X X X X" The interest of the public generally	 is often times too vague and	 generally	 the exercise of discretion deserves to be canalised to guide the statutory bodies and to facilitate better appreciation by the applicants of the claims that may ordinarily be considered by transport tribunals. From this angle	 the Tamil Nadu State has framed rules. expressly subordinated to the paramount factor of public interest which shall weigh with tribunals when adjudging among com peting claimants. 'This Court	 in Kumaraswamy(1)	 summed up the purport of the rule thus: "The system of marks	 under the Rules framed under the Act by the Tamil Nadu Govern ment	 prescribes the various qualifications for applicants for permits for passenger transport under the . Rule 155 A crystallises these considerations and describes them as guiding principles for the grant of stage carriage permits. The rule itself emphasizes what is obvious	 that the paramount consideration of the interest of the public	 as enshrined in Section 47(1)	 must be given full weight while awarding per mits. That means to say that the various factors set out in rule 115 	4 are subject to section 47(1). This is clarified by sub rule (4) of Rule 155 A	 which runs thus: "After marks have been awarded under sub rule (3)	 the applicants shall be ranked according to the total marks obtained by them and the applications shall be disposed of in accordance with the provisions of sub section (1 ) of section 47. " There is no doubt that bus transport is calculated to benefit the public and it is in the fitness of things that the interest of the travelling public is highlighted while evalu ating the relevant worth of the various claim ants. " Rule 155A(3)D(1) offends against the prescription in the proviso (1) 396 to section 47(1 ) and is void	 according to counsel for the appellants. Before examining this alleged vice	 we may as well read sub rule (3) of Rule 155 A to the extent neces sary: "(3) After eliminating in the manner laid down in subrule (2)	 the applicants who are unsuitable	 marks shall be awarded for assessing the different qualifications of the remaining applicants for the grant of permits as follows : (A) Residence Two marks shall be award ed to the applicant who has his principal place of business or permanent residence at either terminus or on the route. Explanation. The term 'principal place of business ' shall mean only the registered headquarters of the company and not the resi dence of the Managing Director or any other Director of the Company. (B) Technical qualification (for Owner or Managing Director). Two marks shall be awarded to the applicant if the Owner or the Managing Director of the organisation has technical qualification which may be useful to run the transport service efficiently. (C) Workshop facilities. Two marks _shall be awarded to the applicant who is in possession of workshop facilities as given in Explanation under item (2)(iv). (D) (i) Five marks shall be awarded to the applicant falling within the proviso to clause (c) of section 62 A of the Motor Vehi cles Act	 1939	 i.e.	 State Government	 Cen tral Government or any Corporation or Company owned by the Central Government or State Government. (ii) The applicant who operates not more than nine stage carriages excluding spare buses	 shall be awarded marks as follows : (1 ) Applicant operating one to three buses 4 marks. (2) Applicant operating four to six buses 3 marks. (3) Applicant operating seven to nine buses 2 marks. Provided that if a new entrant has made an application for a short route other than town service route	 no marks shall be awarded to any applicant under clause (B)	 (C) and (D) (ii). " The ground of invalidation urged is that there is no justification for grant of 5 marks to an applicant falling within r. 155A (3)(D)(1) solely for the reason that it is owned by the State Government. Ownership is irrelevant and the sacrifice of public interest at the altar of government interest is contended to be a flagrant partiality shown by the subordinate legislation in the teeth	 and transgressing the limits	 of the equal consideration implicit in section 47(1 ). second argument 397 (Krishna Iyer	 J.) is that the proviso to section 47(1)	 as amended by Act 48 of 1974 (Tamil Nadu Amendment Act) gives preference to a State Transport Undertaking	 other things being equal	 and im pliedly provides against any larger preference being shown to such an undertaking in the guise of rules. For this reason	 the generosity of the rule being contrary to the narrow preference in the proviso to the section (brought in by later amendment)	 the former cannot co exist with the latter and must be taken as impliedly repealed. Although this amendment to the Act was later than the promulgation of the rules	 the law as it stands today is the basis of our judgment. Thus the two question formulated right at the beginning of the judgment arise in the setting of facts and law we have broadly described above. It was urged by Shri Chitale	 followed by Shri Rama murthy	 in two of the several matters heard together	 that Part IVA provided for monopolistic award of permits to the State Transport Undertaking but Part IV put everyone on a competitive basis	 regardless of whether one was a State undertaking or not	 the most meritorious winning the battle in a free market economy. If the soul of Part IV were free competition	 not 'rigged ' selection	 aid in the shape of extra marks given by rules had to be withdrawn and every applicant had to run without anyone being given a handicap in the race. State undertakings being awarded 5 grace marks for no reason except that they belonged to the State was a gross violation of the spirit and letter of section 4 7 (1 ) which postulated the promotion of public interest as the basic consideration and the selection of the ablest as the criterion for choice. Both counsel	 in their overlapping arguments	 stressed that there was a negative mandate in the proviso to section 47(1) not to prefer a State undertaking save where other conditions were equal and if the State undertak ing was unable to attain the condition of equality with another	 its claim could not be promoted by the artifice of assignment of marks to a State undertaking qua State under taking. Public law	 in our pie bald economy and pluralist socie ty	 responds to societal challenges and constitutional changes. TO miss the ideological thrust of our Constitution and the economic orientation of our nation while construing legislation relating to public law and scanning them for their validity is to fail in understanding the social phi losophy that puts life and meaning into the provisions of the Act. The law	 being realistic	 reckons with the social ist sector covering State and co operative enterprises. The special status of a government owned transport undertaking in a Welfare State is obvious. It has large resources to cater to the traffic needs. It has	 within its range of influence and coordination. many services useful to the travelling public	 which may be beyond the reach of private ownership. Its functional motto is not more profits at any cost but service to citizens first and in a far larger measure than private companies and individuals	 although profitability is also a factor even in public utilities. Its sensitivity to community welfare and en couragement of labour participation	 its accountability to the Government	 the legislature and the public put it in a category by itself. It is socially conscious	 not profit obsessed. We are aware of the shortfalls of some public sector undertakings in some respects 398 but it needs little argument to hold that to classify State transport systems on a separate footing is realsic and is ordinarily no sin before the principle of equality before the law. The legislative body has done	 in the given circum stances	 what it thought was sound policy and we find no vice in the policy. To classify what is conceptually and operationally different into a separate category is intelligence	 not impertinence. The judicial art of interpretation and ap praisal is imbued with creativity and realsm	 especially where fundamental changes have been wrought by the Constitu tion in our approach to public sector enterprises. Legal Darwinism	 adapting the rule of law to new societal develop ments	 so as to survive and serve the social order is neces sary: "That court best serves the law which recognizes that the rules of law which grew up in a remote generation may	 in the fullness of experience	 be found to serve another genera tion badly	 and which discards the old rule when it finds that another rule of law repre sents what should be according to the estab lished and settled judgment of society	 and no considerable property rights have become vested in reliance upon the old rule. It is thus great writers upon the common law have discovered the source and method of its growth	 and in its growth found its health and life. It is not and it should not be station ary. Change of this character should not be left to the legislature. If judges have woefully misinterpreted the mores of their day	 or if the mores of their day are no longer those of ours	 they ought not to tie	 in helpless submission	 the hands of their successors." (Cardozo: The Nature of the Judicial Proc ess: Yale University Press: pp. 151 152). This refreshing perspective guides us to look at the submissions advanced. Both the contentions can be shot down by three considerations. Firstly	 a State enterprise	 in a truly Welfare State	 is charged with a social consciousness and responsibility for its citizens	 an attention to serve them and a willingness to embark on public utility undertak ings better to fulfil people 's demands. The public sector enterprises are expected to be model employers and model servants	 planning their budgets	 subjecting themselves to public audit and criticism and inquest by legislative com mittees and the Houses of the legislature. Profits are their concern but	 more importantly	 public weal is their commitment. Such is the philosophy of the State sector in our socialistic pattern of society. Article 19(6)(ii) and article 38 of the Constitution	 section 47 (1 )	 especially the proviso	 and Charter IVA of the Act (now governed by the impregnable Ninth schedule to the COnstitution) throw light on this policy of the paramount law. Here	 therefore	 the rule making authority	 having regard to all relevant circum stances	 has decided to award to a State Transport Undertak ing 5 marks. This is not an arbitrary stroke of favouritism because there are many promotional factors bearing on the interest of the travelling public which a State enterprise qua State enterprise will	 but a private enterprise qua private enterprise will not	 take care of. 399 (Krishna lyer	 J.) After all	 private enterprise has its primary motivation in profit	 although	 under State direction	 it is becoming socially responsive. The superiority in many respects (not all respects) of State Transport Undertakings	 in the legis lative judgment	 has led to r. 155A. This classification has noetic nexus with and rational relation to the object of augmenting the good of the passenger community. The theory	 rooted in the obsolescent laissez faire economics	 that only cold competition among claimants to run businesses brings out the best operator has serious limitations in fields where the focus is on public service	 not gains of business. Public law	 adapting itself to this socio economic view	 shifts its emphasis. This is what we have earlier called legal Darwinism. We	 therefore	 hold that the assignment of marks under r. 155A is geared to public interest	 which is the desideratum of section 47 ( 1 ) of the Act. We now move on to an examination of the alleged fatal incompatibility between the proviso to section 47(1) and L 155A. This second submission of counsel is a trifle mystifying. There cannot be a contradiction without diction. Unless section 47(1) proviso carries a negative injunction that transport tribunals shall not give any other preferential considera tion than what is stated in it	 there cannot be any con flict between it and the impugned rule. The proviso to the section does nothing of the kind. It merely takes care of a specific situation. Where a State Transport Undertaking: and a private operator are equally balanced	 the scales may be tilted in favour of the former. There is no implied inter dict that in other contingencies no preference shah be accorded. It is not a 'Thus far and no further '. Indeed	 the spirit of this proviso has been carried further by the rule	 having regard to the realities of the total transport system plying in the State. The third consideration which silences the appellant 's charge of violation of section 47 is that the marking formula does not deprive the administrative tribunals of their discretion to choose the best. The consternation of the private entrepreneurs that by manipulating the marking mechanism the State undertaking	 regardless of its demons trable inferiority of public service	 will knock off all the permits	 paralysing the power of the Tribunal to pick and choose	 by the overwhelming and inevitable superiority of marks	 is misplaced. The fear is falsified if we read the rule aright. It has	 written on its face	 its own limita tion. Marks shall guide	 not govern the award. Full discretion	 to some extent	 canalised by the marking proce dure	 still vests in the Transport Authority. For	 the marks	 these authorities will remember	 sway the exercise of judgment	 not supersede it. It is conceivable that the pecularities of a route	 the calamitous performance in an area of a State transport system	 the outstanding spe cial facilities of a particular private operator or other like feature may outweigh the mechanics of marks. After all	 many qualifications	 advantageous to the travelling public	 may be thought of	 untouched by the rigid marking moulds. They are not irrelevant and may still be regarded by the tribunals. All this leads to the conclusion that marks shape but do not clinch the ultimate selection. The public is the consumer; its plenary service is the final test. Therefore	 these is 400 nothing in r. 155A deprivatory of the discretion vested by section 47(1).This interpretative footnote must allay the appre hensions voiced by counsel. Nor are we convinced that there is no possibility of a private operator exceeding the mini mum marks of a State Transport Undertaking. Moreover	 the marking formula lacks flexibility. Merely because the State Transport Undertaking has no 'residence ' or workshop on the route	 although its attention and ability to react are considerable	 why should it suffer a marks created handicap ? There is equity in r. 155A	 making up	 as it does	 for the present shortfalls in the marking system visa visa govern ment transport service. The appeals	 for these reasons	 must suffer dismissal. There will be no order as to costs. BEG	 J. I agree with the conclusion reached by my learned brother Krishna Iyer. As arguments in this batch of cases seem to raise some questions which I	 speaking entire ly for myself	 consider to be really outside the sphere of the law which we have to interpret and apply	 I would like to make some observations on the implications of these questions argued after stating my reasons for agreeing with my learned brother. Mr. Chitaley 's first argument for some of the appellants raised only what may be described as "normal" legal ques tions of construction or interpretation (there is some difference between these two allied processes as will appear from Crawfords "Statutory Construction"	 1940 Edn.	 Chapter 18	 paragraph 157 to 158 pages 240 244)	 as to whether Rule 155A(3)(D)(i)	 reproduced in the judgment of my learned brother Krishna Iyer	 gives effect to or conflicts with Section 47 of the (hereinaf ter referred to as 'the Act '). It was urged by the learned Counsel that what can be done only by resorting to Chapter IV A of the Act	 by framing a scheme for partial or complete nationalisation of the routes involved	 cannot be accom plished by framing a rule only ostensibly purporting to give effect to Section 47(1 ) of the Act or the proviso to it. In ultimate analysis	 the rule of construction relied upon by Mr. Chitaley to make the last mentioned submission is: "Expressio unius est exclusio alterius". This maxim	 which has been described as "a valuable servant but a dan gerous master (per Lopes J.	 in Court of Appeal in Colgu noun vs Brooks(1) finds expression also in a rule	 formu lated in Taylor vs Taylor	(2) applied by the Privy Council in Nazir Ahmad vs King Emperor(3) which	 has been repeat edly adopted by this Court. That rule says that an express ly laid	 down mode of doing something necessarily implies a prohibition of doing it in any other way. The maxim from which the rule in Taylor vs Taylor(supra) is derived and the rule itself were discussed and explained by this Court in the Parbhani Transport Co operative Society Ltd. vs the Regional Transport Authority	 Aurangabad & Ors (4) with specific reference to the argument advanced there that	 (1) at 65. (2) at 430. (3) (1936) L.R. 63 I.A. 372. (4) ; 401 as Chapter IV A is meant for running its own buses by the State by nationalisation of Motor Vehicle Road Transport Services	 it was not open to the State to apply for per mits at all under Chapter IV of the Act which applies to private operators only. This argument	repelled by this Court there has been put forward before us in a somewhat different and attenuated form by Mr. Chitaley. Neverthe less	 the basic rule of interpretation submitted to us is the same as the one which was relied upon in this Court in the Parbhani Transport Co operative Society 's case (supra) in an attempt to exclude the State Transport Undertaking altogether from entry into what was sought to be made out to be the exclusive preserve of private operators. Before us	 it is contended that exclusion of private operators could only be brought about by resorting to a duly framed scheme	 on appropriate grounds given in Section 68C of the Act	 but not indirectly by framing the kind of rule which has the effect of excluding private operators from the sphere of open competition which	 it is submitted postulates an ini tial equality of positions. This argument rests	 as I will indicate below	 on two erroneous assumptions: firstly	 that Rule 155A(3)(D)(i) has the effect of excluding private operators; and	 secondly	 that the proviso to section 47(1) compels the permit issuing authorities to postulate or start by assuming an equality of conditions	 as between private operators and a State Transport Undertaking. Indeed	 if they were to start with the assumption of equality they will have to give preference to the State Transport Under taking straightaway because that is what the proviso re quires. The mainstay of the arguments of learned Counsel for the appellants before us	 however	 is that Rule 155A(3)(D)(i) really has the effect of excluding the private operators altogether by making it impossible for them to ever obtain preference over the State Transport Undertak ing when it applies for a permit in competition against them. The reply on behalf of the State is that no exclusion of private operators is either intended or brought about by an application of Rule 155A(3)(D)(i) of the Act. On the other hand	 it is submitted that	 as an ordinary operator and a State Transport Undertaking are	 in many ways	 so unlike each other that	 unless five marks were assigned to each application of the State Transport Undertaking	 it could not compete at all	 on a fair and equal footing	 with pri vate operators	 who are able to obtain straightaway two marks for residential qualifications	 four marks if they are operating not more than three buses	 and two marks for workshop facilities. apparently	 the residential qualifica tion has reference to residence within the area in which the motor vehicles are to ply	 and marks workshop facilities are granted to operators who are able to show such facili ties on particular routes whereas the State Transport Undertakings	 it is pointed out	 will neither have a resi dence within such an area nor may be able to show	 in a particular case	 workshop facilities on particular routes even though they may have better workshop facilities on the whole. Again	 two marks are to be given to private concerns or organisations	 plying on particular routes	 if their owners or Managing Directors have certain technical qualifications. It is pointed out that	 as State Transport Undertakings do 402 not have individual owners or Managing Directors	 for whom these marks could be allotted	 even though they may have technically much better qualified personnel to attend to their motor vehicles	 the impugned Rule 155A(3)(D)(D could be justified as meant only to place State Transport Under takings on a footing of possible equality with private operators in competing. for permits to be granted under Section 47(1) read with Section 42(3) of the Act and to do no more. Furthermore	 Rule 155A(3)(D)(i) occurs in a group for marks to be assigned on the basis of the number of vehicles run by the operators. In any case	 it was submit ted that it is a fair provision as a rough guide but is not decisive by any means. It seems to me that the conten tion advanced on behalf of the State that the impugned part of Rule 155A enables provisions of the proviso to Section 47(1)	 read with Section 42(3)	 to be worked a manner in which the statutory provisions were intended to overate and does not really authorise a circumvention or infringement of the provisions of Chapter IV of the Act	 is well founded. The manner in which provisions of Chapter IV of the Act were meant to operate in cases of competition between pri vate operators and State Undertakings was explained in the Parbhani Transport Co operative Society 's case (supra) as follows (at p. 184): "The Government has of course the power to do. any business it lies and therefore the business Of running stage carriages. We have earlier drawn attention to the change made in cl. (a) of section 42(3) by the: amendment of 1956. Previously	 it was not necessary for the Government to obtain permits under section 42(1) for buses that it intended to run as stage carriages. SinCe the amendment the Government can no longer run transport vehicles for commercial purposes without obtaining permits under section 42(1 ). Now the plying of buses as	 stage carriages is a commercial enterprise and for such buses	 therefore	 under the sections as they stand	 the Government would re quire permits as any one else. That being so	 the sections clearly	 contemplate that the Government may apply for and obtain permits for its buses run as stage car riages. The rule applied in Nazir Ahmad 's case (1936) L.R. 63	 I.A. 372	 381) does not permit the ordinary meaning of section 42	 sub. s.(1) and sub. s.(3)	 el. (a) to be cut down because of the provisions of Chapter IVA. The Act lays down two independent sets of provisions in regard to the. running of buses by the Government	 one under Chapter IV and	 the other under Chapter IVA. Chapter IVA was intended to give the Government	 a special advantage. When the Government chooses to proceed under that chapter	 it becomes entitled as a matter of right under section 68F(1 ) to the necessary permits. Under Chapter IV the Government does not have any such advan tage; it has to compete with other applicants	 to secure permits to be able to run its buses. The powers under the two. chapters are there fore different. To such a case the principle of Nazir Ahmad 's case cannot be applied". 403 Both Chapters IV and IVA enable plying of State transport as well as privately owned vehicles on hire on same routes	 but the grounds for these combined operations under the two chapters are different. The governing principle of Section 47(1) is to preserve as free and open a competition as possible in public interest	 whereas the reason for allowing private operators upon a nationalised route may be broader one of public policy which may favour a decision against sudden stoppage of privately provided motor trans port	 so as to avoid wastage of national wealth	 even though it takes the form of investments by individual entrepre neurs	 or	 its object may even be prevention of undue hard ship to private operators. Other reasons for permit ting combined services can be. given. It is	 however	 possible only under Chapter IVA to exclude private operators completely. But	 unless any rule relating to provision of motor transport under chapter IV has that effect it cannot be asserted that what can be done only by resorting to Chapter IVA is being attempted under the provisions of Chapter IV. The rule in Nazir Ahmad 's case (supra) applies only to cases where there is a single specified mode laid down for doing something in exercise of the legal power to do it. In that event	 the specified mode may	 negatively	 operate as a prohibition against what is not prescribed at all and is outside the statute. But	 it could not apply to a case where two modes of doing the same thing are provided for by a statute itself. Nor	 as I have indicated above	 could it be said that what is to be done under Chapter IV and what can be done under a scheme under Chapter IVA are really the same simply because	 in a given case	 the results of both may appear to be similar or even identical. Mr. Ramamurthi	 appearing on behalf of some of the appellants	 embarked on quite an ambitious argument built upon an elaboration of the theme that Chapters IV and IVA belong to two different fields or spheres of action which cannot	 so to speak	 be allowed to mix	 overlap	 or collide. It was contended that the waters of what are	 in the eye of law	 two different streams of activity. must not be allowed to mingle. If 1 am not mistaken	 even the word "pollute" was used	 in the flow of arguments	 to describe	 possibly in a light vein	 the alleged inequity of an invasion by a State Transport Undertaking of the supposedly exclusive preserve of private enterprise. It was suggested that such a result would involve "pollution" of the domain of open competition	 which is forbidden territory for State Under takings introduced as a consequence of another ideology or sphere of action found in Chapter IVA. It seems to me that to hear such an argument	 advanced even in a lighter vein	 is really rather surprising in view of the language of the statute and welt known facts to which it is related. It is quite well known that ours is what is known as a "mixed economy". The highest norms of our law are embodied in our Constitution. Article 19(6)(ii) of the Constitution clearly contemplates: "the carrying on by the State	 or by a Corporation or controlled by the State	 of any trade	 business	 industry or service	 whether to the exclusion	 complete or partial	 of citizens or. otherwise". And	 in order to fulfil the objectives of the Preamble. to our Constitution	 the Constitu 404 tional mandate	 contained in Article 39(c) of the Constitu tion	 which the State has to carry out	 may make it impera tive upon the State	 in appropriate circumstances	 either to take over or nationalise motor transport on roads in any region or area completely or to supplement the Transport Services provided by private operators with those provided by the State. It seems to me that neither Chapter IV nor Chapter IV A can be really put into two separate water tight compartments so as to make it imperative either to exclude State Transport Undertakings from operating under the provi sions of Chapter IV or to exclude private operators when a scheme under Chapter IV A	 which may itself provide for only a partial exclusion of such operators	 is in force. In the face of the clear words of proviso to Section 47 (1 ) of the Act	 enabling State Transport Undertakings to provide Transport facilities in open competition	 and of Section 68(C) in Chapter IV A of the Act	 enabling "the exclusion complete or partial" of private operators from particular areas or routes	 such an argument cannot be put forward at all before us under some preconceived notions even after these very notions had been rejected by this Court in the Parbhani Transport Co operative Society Ltd 's case (supra). It is clear that the two chapters of the same Act are both intended to subserve "the interest of the public gener ally" in any area in the country	 That is the integrating or governing principle evident from the language of the Act itself in both Chapter IV and Chapter lV A of the Act. An argument advanced on behalf of the appellant seemed to be that Rule 155A(3)(D)(i) results in defeating the mandate of Section 47(1) of the Act	 that the Regional Transport Authority must	 as explained repeatedly by this Court	 keep "the interest of the public generally" in the fore front. As already indicated by me	 this argument really proceeds on the erroneous assumption that the mere fact that the State Transport Vehicles are given five marks would defeat public interest by excluding consideration of all facts except that the State Undertaking has applied for one or more permits on a particular route. As my learned brother Krishna Iyer has also pointed out	 this is an unwarranted assumption. Rule 155A gives only guidance	 but the totality of factors men tioned in Section 47(1) 'really decide. It was suggested on behalf of the State Transport Under taking that the obvious capacity of a State Undertaking to provide facilities which are beyond the reach of private operators	 that its actions are subjected to such constant	 vigilant	 and rigorous control on behalf of the public	 and that it is bound to be so free from any desire to make profit.s	 by sacrificing public interests or convenience of passengers that	 even if nothing else was considered	 these presumed advantages would justify the award of five marks on each application of the State Undertaking for a permit. If this line of reasoning was completely accepted and car ried to its logical conclusion	 the provision/or giving five marks 	to each application of the State Undertaking would become quite otiose or unnecessary because	 in that case	 the State Undertaking would	 by relying merely on a presumed superiority for purposes of Section 47 (1 )	 get a prefer ence automatically. The proviso to Section 47 (1 ) of the Act would then	 apart from making it clear that the State Undertaking can also apply for permits	 for which 405 purpose Section 42(3) was enough	 serve: no useful purpose. Indeed	 if such a view were to be accepted	 the first part of the proviso to Section 47 (1 ) would seem to rest on a false premise because there could be no case in which "other conditions" could ever be "equal" as between a State Transport Undertaking and a private operator. The State Transport Service would	 in that case	 always get a prefer ence. For this reason	 I do not think that this line of reasoning could be pushed too far. It has to be assumed	 in view of the opening words of the proviso to section 47 (1 )	 that there may be cases in which an application of the basic principle	 contained in Section 47 (1) of the Act	 may tilt the balance either in favour of the State Undertaking or the private operator. The proviso applies only where the State Undertaking could ' reasonably be deemed to be in a position of equality as regards comparative advantages offered by it. As there cannot	 between such dis similar operating units	 be comparability of conditions or advan tages offered unless some rule is flamed and applied which could make comparison reasonably possible	 it seems to me that Rule 155A(3) (D)(i) is justifiable on the ground that it makes what is legally contemplated and permissible also practicable. The proviso. to Section 47 (1 ) reads as follows: "Provided that other conditions being equal	 an application for a stage carriage permit from any State Transport Undertaking or a co operative Society registered or deemed to have been registered under any enactment in force for the time being shall	 as far as may be	 be given preference over applications from individual owners. " An examination of this proviso shows that an. equality of other conditions is contemplated before any question of giving preference	 merely on the ground that the applicant is the State Transport Undertaking or a Cooperative Society	 can arise. If other conditions are equal	 then	 undoubted ly	 the choice as between such equals must	 if the proviso is to be given effect	 be made in favour of the State Trans port Undertaking or a Cooperative Society automatically. That is how	 in such a case	 See. 47(1) itself would be deemed to operate. The validity of the proviso is not challenged. Even if Article 14 were available for an attack upon it	 as it is not during the current emergency	 it is clear that the State Transport Undertaking does stand in a separate category. Therefore	 it could be found entitled	 for obviously good and intelligible reasons	 to preference over private operators "other conditions being equal". The narrow ques tion before us. Thus	 appears to me to be nothing more than whether the impugned part of Rule 155A sub serves or vio lates the proviso. The proviso itself is meant to explain what public interest	 as visualised by Section 47(1)	 re quires. Hence it appears to me that the validity of the impugned part of Rule 155A could be determined on purely legal grounds as a necessary corollary of the proviso to Section 47(1). The impugned part of the Rule is there to make the proviso workable and not to defeat its provisions. 406 It is	 however	 becoming increasingly fashionable to start with some` theory of what is basic to a provision or a chapter or in a statute or even to our Constitution in order to interpret and determine the meaning of a particular provision or rule made to sub serve an assumed "basic" requirement. I think that this novel method of construc tion puts	 if I may say so	 the cart before the horse. It is apt to seriously mislead us unless the tendency to use such a mode of construction is checked or corrected by this Court. What is basic for a section or a chapter in a stat ute is provided: firstly	 by the words used in the statute itself; secondly	 by the context in which a provision oc curs	 or	 in other words	 by reading the statute as a whole; thirdly	 by the preamble which could supply the "key" to the meaning of the statute in cases of uncertainty or doubt; and	 fourthly	 where some further aid to construction may still be needed to resolve an uncertainty by the legislative history which discloses the wider context or perspective in which a provision was made to meet a particular need or to satisfy a particular purpose. The last mentioned method consists of an application of the Mischief Rule laid down in Heydon 's case long ago. If we start from a theory as to. what the real purpose or need is or could be	 the danger is that we may be inject ing a subjective notion or purpose of our own into what is	 after all	 a legal question of construction or interpreta tion	 according to well recognised principles	 although it may be necessary	 in exceptional eases	 to explain or forti fy the interpretation adopted in the light of so well under stood and. well known a purpose or theory that we could take judicial notice of it and refer to it. The exposition of the well known purpose or theoretical foundation must	 however	 generally	 flow from and explain an interpretation adopted	 on the strength of legally acceptable and accepted canons of construction	 if we are to avoid the danger of an a priori determination of the meaning of a provision based on our own pre conceived notions of an ideological structure or scheme into which the provision to be interpreted is somehow fitted. The path of judicial certainty and predictability has to be paved with well settled principles of construction and interpretation. We cannot let it develop into a slippery slope be set with hazardous possibilities. The science of statutory construc tion and interpretation I think can call it that rests on certain systematised principles and rules of common sense	 logic	 and reason. It can not be transformed into a happy hunting ground for whatever may captivate the forensic or judicial fancy or become something akin to poetry without even the attractions of euphony. For the reasons given above	 I find that	 on an applica tion of the ordinary and well recognised rules of interpre tation	 without resorting to any of the novel methods suggested by some of the arguments of learned Counsel for the appellants	 the impugned part of Rule 155A(3) (D)(i) is valid. I	 therefore	 concur with nay learned brother Krishna Iyer	 and hold that the connected appeals and peti tions before us must be dismissed. M.R. Appeals dis missed.

The appellants	 private stage carriage operators	 applied for the renewal of their expiring bus permits. The re spondent State Transport Undertaking objected	 urging preferential grounds in its own favour	 claiming to have secured higher marks with the aid of r. 155 A of the Motor Vehicles Rules. The State Transport Undertakings claim was upheld. The appellants moved the appellate Tribunal	 and also filed a writ petition before the High Court for direc tions to the appellate Tribunal to dispose of his appeal without relying on r. 155 A. The writ petition was dismissed by a Single Judge	 and an appeal before the Division Bench also failed. In appeal by Special Leave	 the appellants assailed the validity of r. 155 A the grounds of its being partial to the Government against public interest and contradicting the proviso to section 47(1) of the . Dismissing the appeals	 the Court	 HELD: (Per Krishna Iyer J. for himself and on behalf of A. N. Ray CJ.) 1. The assignment of marks under r. 155 A is geared to public interest	 which h the desideratum of section 47(1) of the Act. This is not an arbitrary stroke favouritism because there are many promotional factors bearing on the inter est of the travelling public which a State enterprise qua State enterprise will	 but a private enterprise qua private enterprise will not take care of. There is equity in r. 155 A	 making up	 as it does	 for the present short.falls in the making system vis a vis a government transport service. [398H. 399B] P. Kumaraswamy vs State Transport 	Appellate Tribunal	 Madras & referred to. The Court observed: Legal Darwinism	 adapting the rule of law to new socie tal developments	 so as to survive and serve the social order	 is necessary. [398B] Cardozo: The nature of the Judicial Process; Yale Uni versity Press; pp. 151 152	 relied upon. There cannot be any conflict between section 47(1) proviso and the impugned rule. The proviso does not carry any negative injunction that transport tribunal shall not give any other preferential consideration than what is stated in it. There is no implied interdict that in other contingen cies no preference shah be accorded. The proviso merely takes care of a specific situation. Moreover. the mark ing formula does not deprive the administrative tribunals their discretion to choose the best [399C E] Per H.M. Beg	 1. (Concurring) Where there is a single specified mode laid down for doing something exercise of the legal power to do it	 the specified mode may	 negatively operate. 393 (Krishna Iyer	 J.) as a prohibition against what is not prescribed at all and is outside the statute. But expressio unius est exclusio alterius could not apply ot a case where two modes of doing the same thing are provided for by a statute itself. Here both chapters IV and IV A enable plying of State transport as well as privately owned vehicles on hire on same routes	 but the grounds for these combined operations under the two chapters are different. [403A	 C	 D] Parbhani Transport Co operative SOciety Ltd.	 vs The Regional Transport Authority	 Aurangabad & Ors. ; 	 applied. Nazir Ahmad vs King Emperor (1936) L.R. 63 I.A. 372	 distin guished. Colquhoun vs Brooks at a	 65; Taylor vs Taylor at 430 and Crawfords "Statuto ry Construction" 1940 Edn.	 Chapter 18	 paragraphs 157 to 158	 pages 240 244	 referred to.