McGowan Emerson/Thoreau

In "Nature", Emerson sees human perfectibility through man's integration with nature and subsequent accomplishments thereof. Emerson's pantheistic view of the world is seen through his constant allusion to a certain universality that can only be grasped by an elite few: "To speak truly, few adult persons can see nature. Most persons do not see the sun. At least they have a very superficial seeing." What Emerson is suggesting here and further establishes throughout this piece is the distinction between seeing and understanding. Emerson goes on to explain that while one might see the sun, one does not necessarily conceive of its function of illuminating everything and therefore giving a meaning to vision itself, "And as the eye is the best composer, so light is the first of painters. There is no object so foul that intense light will not make beautiful. And the stimulus it affords to the sense, and a sort of infinitude which it hath, like space and time, make all matter gay."Here, Emerson is essentially saying that perception is what you make of it. Emerson would hold that the ability to perceive something in terms of its universality is to perceive it purely and perfectly; but perfectibility in perception is only prerequisite to whole human perfectibility, which is determined by creation."Whilst the abstract question occupies your intellect, nature brings it in the concrete to be solved by your hands. . . Build, therefore, your own world. As fast as you conform your life to the pure idea in your mind, that will unfold its great proportions. A correspondent revolution in things will attend the influx of the spirit." Here, we see that Emerson sees human perfectibility as the successful construction of a life, which best represents the purity and universality of nature as perceived correctly. 
As Emerson focuses on nature as a haven for human perfectibility, Thoreau holds the American government (civilization, arguably opposite of nature) accountable for continual corruption. Thoreau is extremely reliant on the inner workings of human beings rather than federal regulation and control as a mechanism for morality and perfection, specifically citing the existence of the human conscience. He argues that the problem with American people is that, "After the first blush of sin comes its indifference; and from immoral it becomes, as it were, unmoral, and not quite unnecessary to that life which we have made." What Thoreau is contending here is that Americans choose to blindly accept rather than correctly act upon the corrupt elements of the government such as slavery and the war against Mexico simply because it is the government. Thoreau argues that we should answer to our conscience as the number one moral authority rather than to the government. This kind of thought suggests human perfectibility because it promotes self reliance in the purest sense: "They who know of no purer sources of truth, who have traced up its stream no higher, stand, and wisely stand, by the Bible and the Constitution, and drink at it there with reverence and humanity; but they who behold where it comes trickling into this lake or that pool, gird up their loins once more, and continue their pilgrimage toward its fountainhead."What Thoreau is suggesting here is not the essentiality, but rather the acute possibility of human perfection. He sees it as a struggle against the inevitable existence of corruption, which is illustrated by the body of water, which is full of false doctrines other than those which should be exclusively lived by: The Bible and The Constitution.