Question
What are the four legs of Dharma?
Answer
No, the four legs of the bull of Dharma do not represent percentages of righteousness in society (although it is true that the number of righteous people decline as the Yugas progress). Rather, the legs represent different virtuous qualities any individual can have. Here is what Arjuna's grandson Parikshit says in the Srimad Bhagavatam, upon seeing the bull of Dharma standing on one leg at the start of the Kali Yuga:
In the age of Satya your four legs were established by the four principles of austerity, cleanliness, mercy and truthfulness. But it appears that three of your legs are broken due to rampant irreligion in the form of pride, lust for women, and intoxication. You are now standing on one leg only, which is your truthfulness, and you are somehow or other hobbling along. But ... [Kali], flourishing by deceit, is also trying to destroy that leg.
So to sum up, in the Satya Yuga, the bull of Dharma starts out with four legs: Tapas or austerity, Shaucha or cleanliness, Daya or mercy, and Satya or truth. By the start of the Treta Yuga, austerity is gone, and by the start of the Dwapara Yuga cleanliness is gone. Finally, by the time the Kali Yuga comes, only one leg is left standing, namely truth, and even truth is steadily eroded as the Kali Yuga progresses.
By the way, on a positive note, Parikshit was able to re-establish the legs of Dharma in the Kali Yuga, by banishing the Kali Yuga into a limited number of places:
Mahārāja Parīkṣit, thus being petitioned by the personality of Kali, gave him permission to reside in places where gambling, drinking, prostitution and animal slaughter were performed. The personality of Kali asked for something more, and because of his begging, the King gave him permission to live where there is gold because wherever there is gold there is also falsity, intoxication, lust, envy and enmity. Thus the personality of Kali, by the directions of Mahārāja Parīkṣit, the son of Uttarā, was allowed to live in those five places. Therefore, whoever desires progressive well-being, especially kings, religionists, public leaders, brāhmaṇas and sannyāsīs, should never come in contact with the four above-mentioned irreligious principles. Thereafter the King reestablished the lost legs of the personality of religion [the bull], and by encouraging activities he sufficiently improved the condition of the earth.
So as long as you avoid those five things, the negative effects Kali Yuga won't be present. And as I discuss in this answer, the Kali Yuga has its own benefits, like the ability to achieve great results simply by chanting the name of Vishnu.
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