how to determine the right law

९ युधिष्टिर
      प्रत्यक्षं लोकतः सिद्धम् लोकाश्चागम पूर्वकाः
      शिष्टाचारो बहुविधो ब्रूहि तन् मे पितामह
  १० भीष्म
     धर्मस्य ह्रियमाणस्य बलवद्भिर् दुरात्मभिः
     संस्थायत्नैर् अपि कृता कालेन परिभिद्यते
 ११ अधर्मा धर्मरूपेण तेणैः कूपा इवावृताः
     ततस्तैर् भिद्यते वृत्तम् शृणु चैव युधिष्ठिर
 १२ अवृत्त्या ये च भिन्दन्ति श्रुतत्यागपरायणाः
     धर्मविद्वेषिणो मन्दा इत्युक्तास्ते न सम्शयाः
 १३ अतृप्यन्तस्तु साधूनाम् य एवागम बुद्धयः
     परमित्येव संतुष्टास्तान् उपासस्व च पृच्छ च
 १४ कामार्थौ पृष्ठताः कृत्वा लोभमोहानुसारिणौ
     धर्म इत्येव सम्बुद्धातान् उपासस्व च पृच्छ च
 १५ न तेषाम् भिद्यते वृत्तम् यज्ञस्वाध्यायकर्मभिः
     आचाराः कारणम् चैव धर्मश्चैवत्रयम् पुनः
9 yudhiṣṭira
      pratyakṣaṁ lokataḥ siddham lokāścāgama pūrvakāaḥ
      śiṣṭācāro bahuvidho brūhi tan me pitāmaha
  10 bhīṣma
     dharmasya hriyamāṇasya balavadbhir durātmabhiaḥ
     saṁsthāyatnair api kṛtā kālena paribhidyate
 11 adharmā dharmarūpeṇa teṇaiaḥ kūpā ivāvṛtāaḥ
     tatastair bhidyate vṛttam śṛṇu caiva yudhiṣṭhira
 12 avṛttyā ye ca bhindanti śrutatyāgaparāyaṇāaḥ
     dharmavidveṣiṇo mandā ityuktāste na samśayāḥ
 13 atṛpyantastu sādhūnām ya evāgama buddhayaḥ
     paramityeva saṁtuṣṭāstān upāsasva ca pṛccha ca
 14 kāmārthau pṛṣṭhatāḥ kṛtvā lobhamohānusāriṇau
     dharma ityeva sambuddhātān upāsasva ca pṛccha ca
 15 na teṣām bhidyate vṛttam yajñasvādhyāyakarmabhiaḥ
     ācārāḥ kāraṇam caiva dharmaścaivatrayam punaḥ


MahabharathamYudhistira asks Bheeshma 
'Tell me, O grandsire, which among these (four) is most authoritative, viz., direct perception, inference from observation, the science of Agama or scriptures, and diverse kinds of practices that distinguish the good.'

"Bhishma said, 'While Righteousness is sought to be destroyed by wicked persons possessed of great might, it is capable of being protected for the time being by those that are good exerting themselves to the best of their capabilities  with care and earnestness.

 Such protection, however, may not hold fast  in the long run, for destruction does overtake Righteousness at the end. 

Then, again, Righteousness often proves a mask for covering Unrighteousness, like grass and straw covering the mouth of a deep pit and concealing it from the view.

 Hear, again, O Yudhisthira! In consequence of this, the practices of the good are interfered with and destroyed by the wicked. 

Those persons who are of evil conduct, who discard the Srutis--indeed, those wicked wights who are haters of Righteousness,--destroy that good course of conduct (which could otherwise be set up as a standard). Hence, doubts attach to direct perception, inference, and good conduct.  

Those, therefore, among the good that are possessed of understanding born of (or cleansed by) the scriptures and that are ever contented, are to be regarded as the foremost. Let those that are anxious and deprived of tranquility of soul, approach these.

 Indeed, O Yudhishthira., do thou pay court to them and seek of them the solutions of thy doubt! 

Disregarding both pleasure and wealth which always follow cupidity and awakened into the belief that only Righteousness should be sought, do thou, O Yudhishthira, wait upon and ask those persons (for enlightening thyself). 

The conduct of those persons never goes wrong or meets with destruction, as also their sacrifices and Vedic study and rites

. Indeed, these three, viz., conduct as consisting of overt acts, behaviour in respect of (mental) purity, and the Vedas together constitute Righteousness.'

In the anusaasika parva  these questions are raised by yudhistira to bheeshma,  under the advise of Lord Krishna himself.  The enforcers of law have a tendency to hold on to citations favourable to them and their interests and by passage of time the original fundamental principles get obliterated.  In such situations reference to the original texts and taking the advise of the impartial judges alone is the right way.  Sticking to redundant precedents will often given benefit only to vested interest.  This is relevant as an argument even in a modern court of law.