epistemology (the study of how we come to know what we know, and the limits of that knowledge) in the European tradition has largely focused on whether and how humans, limited by their subjective nature, can come to know with confidence an objective world.
Of course this assumes that there is an objective world we can perceive. To Plato, the material world we might hope to know is little more than shadows of some more important realm of forms. The reality is in the pattern, not in the thing itself.
By the time of the early philosophers of science, this notion was being transformed. Galileo said we perceive the characteristics of material things, but can only infer their essence. Thus he says beeswax may be yellow, soft when heated by the hand, and smell of honey, but none of that tells us what wax is.
Descarte and Hume took this argument further, saying we could be sure about little (Descarte) or nothing (Hume) of the material world without some kind of divine intervention. Kant provided an interesting alternative, suggesting (like Galileo) that we perceive information coming from the material world, but must evaluate it by category before assembling it into a cogent picture. In fact this does seems a lot like what current brain studies suggest.
But the point of course is that something separates the individual subject from objective knowledge. Followers of Ayn Rand notwithstanding, no one claims that an individual can have total, accurate knowledge of the world. Even if when that quality of knowledge is available through rigorous scientific study, no one carries a laboratory around just to check the weather.
This problem is not limited to philosophical debates. Since the discovery of quantum mechanics, physicists have been troubled by a difficulty separating the influence of their presence from the results of their experiments. Some argue that it is impossible to make that separation. Social scientists have long faced a similar dilemma.
If that sounds like we are doomed to uncertainty, consider that we seem to function without giving it a second thought. How is that? Without getting too deeply into it, we think that that one answer might be we learn to make assumptions. By trial and error an infant growing into a child growing into an adult comes to expect consistency – we only need to experience ice a few times to know it’s likely to always be cold.
Further, we think it follows that people come to rely on their parents, family members, teachers and peers, even strangers. It gets beyond strict epistemology, but we might say one mechanism people use to achieve a working knowledge of the world is human culture. Society allows them to compare evidence within the group, and to receive information without having to test it.
So (for example) people might feel more confident about taking an action if it is supported by the judgment of others. It may be difficult to guarantee that the information is accurate, but people do the best they can with what they have. And don’t think about it very much.
We might say that much of what individuals do on any given day either depends on or is a part of some kind of collective subjective action, in other words subjective decisions supported by the subjective opinions of others. In fact it could be argued that human culture is just another way of saying the same thing, that people exist as social animals within that collective subjective.
But it doesn’t have to be that general; take two examples. For one, people delegate the job of deciding justice to twelve proxies typically chosen at random from the list of registered voters. While the justice system is far from perfect it is fairly reliable, and normal expectations of fairness don’t require our constant personal involvement to confirm.
Another basic form of collective subjective action is the economy. Most specifically, we can argue that the price setting mechanism of markets as a form of collective subjective.