The Path of Humanity was the favored "good" path in Vampire: The Masquerade. It was usually only called "path" by players who downplayed its importance while the cannonical corerules portrayed it as litteral universal humanity of all cultures and individuals in the world of darkness.
The path of humanity is an moral code that sees humanity as an symbol not of human behaviour of both "good" and "bad",nor of human instincts. Instead "humanity" as humanity as humans should be as opposed to animals, impulsivity and non-traditional modern life-style. Path of humanity represents the assumed normal values in society such as compassion for human life, tendency for religion or for respect for society. It is basically a measure goodness and denial of ones desires and selfishness. Path of humanity is not an actual measure of goodness just as it is often said that path of humanity is more morally relative than the paths according those who favour it. It is a measure of degrees of evil measured as falling from an ideal normal human state. Therefore it is the moral code that one has but do not follow because it's all about recognising that the player are not human in the real world. Mark *Raign Hagen wrote in his afterwords in 1st edition that he meant to accuse the player. The point of the path is to regret onces realised guilt of what the character would do anyway. The theme of the game is the human control over the orginal sin which is replaced as the imaginary evil of vampirism. This was called "the beast of all things" in 1st edition and in revised was just the vampiric beast. This is why paths of alternative codes are often unpopular among older vampire players. If there are alternative morals then there is no need to measure degrees of compassion in vampires without compassion. In second edition humanity became more proactive and intentional because it was just as likely to to discover degrees of inhuman paths now seen as personality chategories in the characters.
Humanity represents evil as an degree of what is left of onesgoodness because the path is based on quilt and degeneration into the natural state of ones body seen as an "Rabula Rasa". The very soul of the individual is the conscience it self and path of humanity is about the moral identity cricis when the vampire realise he is a monster and no longer the human that he/she once was.
The path of humanity was introduced in the 1st edition vampire:the masquerade where it was the only path until the second edition. In the 1st edition the path was very clearcut and simple. There is an difference between good in humanity and evil animals. In the second edition the path lost some of it's clearity due to contrast with other paths. Now path of humanity was called "a path" among others. Morality was relative and it was usually as likely for a character to get another path as to keep humanity just by motivation that the character was thinking that way or was a certain kind of personality. This lead to the dharmas in Kindred of the East where alternative codes where standard for vampires and based more on personality traits than before. This also lead to the first edition of vampire:dark ages where a new type of paths called vias or roads where introduced. It was explained that sabbat paths of enlightenment where inhuman because of that sects corruption and that older paths where more human. Humanity was a via among other vias and all vias even the infernal Via Diabolis and the road of the beast functioned like humanity. In the first edition dark ages corebook there was no human versus inhuman difference between the vias and most vias where based on humans codes and personalities before the embrace. It was also clairly stated in this book that degenerating from one via to another only lead to the automatic switch to a more suitable via. Falling to the beast almost always just lead to adopting the road of the beast. In the modern second edition setting of vampire all paths had an common anathema and it was harder to leave humanity and adopt an path which required that you lost all you humanity.Those alternative inhuman codes where also endangered by the madness of the beast. Road of humanity was mostly a road of compassion that struggled with realiy. In revised vampire:the masquerade and in revised vampire:dark ages the difference between humanity and other codes was made stronger. Humanity became once again the dominant universal code of morality instead of an personality trait or intentional moral opinion of the character. Humanity is now more relative and represents many different personal codes or other cultures that are all measures as degrees of humanity. Paths,dharmas and vias are re-cast as artifical intellectual thinking systems and more penalised than before while humanity is more intuitive and irrationally always normal and represents the decided practial moral reality. Storytellers are encouraged to make their own versions of humanity in the Storytellers handbook. Paths of enlightenment and dharmas are now always read in an inhuman and evil way and their philosophical concepts are never read in human real world terms. Paths of enlightenment now have another scale than humanity while before they also had sames degrees now only humanity has degrees because it's "human" and each level in a path are absolute. Paths of enlighenment the same degree like dharma. Having 1 to 3 levels are standard and there are now age restrictions so learning a path takes several years. To have more than 5 in a path in nearly incredible for anyone but an elder.
In general one could say that the path of humanity became more abstract and universal in the revised edition of vampire:the masquerade.