Conclusions in a Weltanschauung depend on argument and aesthetic appeal, but also important are the set of mental constructs that provide a frame in which to percieve the discussion. These frameworks layer on each other from domain-specific to general perception and eventually into the usually-unexamined foundations of a framework of knowledge. Practically, people with very different (or sparse) underpinnings can often still function similarly within the confines of a discipline - a particular lawyer, scientist, or historian might be realist or antirealist, morally objectivist or relativist and still function in that discipline even if they disagree with their colleagues on the deeper meaning of their work. This is the case because of the layered nature of epistemology - while a particular practical epistemology may be required (or useful) within a certain field, the divisions between layers can be bridged in ways that largely mask the difference.
Certainty is a major topic in epistemology - it is a scalar quality describing the degree to which we consider a proposition likely to be true. Truth as a property takes different meanings depending on the context in which it is used - mathematical truths are different in nature than things we call true about the natural world. If we are to be as careful as we can in the construction of our system of epistemology, we build a tower of positions, shedding a bit of certainty at each stage in exchange for power - each layer could take several forms, and later we may find that we may have built multiple incompatible layers at some level as we divide our certainty, layering some of our later yet layers on top of one branch and others on another - this might demand a reconciliation, although to a certain extent hedging one's metaphysical bets is healthy.
Before we have built the least amount of uncertainty or layers into our structure, we find ourself concerned with whether our mind exists. It may seem self-evident that it does if we are returning to foundations from a later commonsense notion of the world and to neglect this layer, but we in fact must consider the possibility that even the us is an illusion and make our first trade of certainty to move past it. This is not on the face of it a very interesting supposition, as foundational as it is - building frameworks on a substantially and functionally different alternative is challenging. To build a functional viewpoint, we take our first foundational stance that our mind exists.
At our second step, we are faced with the perspective of Solipsism and the external world - do we believe there to be an external world independent of our perception? This is a much more interesting distinction - the question of what a world is becomes relevant (although we explore it more in depth in later stages). We could build frameworks in which our entire existence lies within our imagination, and like with the first step we have no means to know ourselves or the universe well enough for a conclusive answer. Pragmatically, we decide that it is necessary to place another uncertain block on top of our first.
At this point, we have the height needed to build some definitions that we start to use to structure our epistemology. We establish two categories into which we can place some of our thoughts (many will be in neither) - thoughts about truth and thoughts about values. This is only one of the many frameworks of truth which we will eventually have, but it is important here - we consider statements to be true to the extent that they corrispond or do not corrispond to the apparent world. For this, we adopt the terminology of "believe" and "is" (in its non-metaphorical most-careful sense). For thoughts about values, their not being apparent in the nature of things, we use the terminology of "hold" (and perhaps a metaphorical "is"). For lack of a method, even in theory, to reach value truth through reason, we at this stage become temporarily value-relativist (I never find reason to remove this from my value framework and develop this relativism considerably further, although later framework decisions may cause others to revisit this matter).
At this point, we are drawn to the distinction between an apparent universe and an actual one - rather than the earlier true solipsism where we are concerned with if there is anything outside of ourself, we ask ourself if our apparent universe is real. There are many ways to formulate these concepts and again a lack of a means by which we might know (at least at this point and possibly ever) whether we are in a real universe, a brain in a jar, or a simulation. We might decide on a definitive stance on the matter, but being risk-averse, the most conservative choice we can make at this point is in fact to largely duck the question - we decide that it does not matter whether our apparent universe is real (and thus don't need to worry about what real means in that context) by noting that whatever our apparent universe is, we live in it and can make sense of it regardless of questions of its realism. Prior to a reexamination and demand for definition, we likely would've worked under an assumption that our universe is real with only a vague intuition on what that realness means - this exercise moves us to a more mentally rigourous position that is nontheless functionally very similar to our original one.
Our next issue concerns how our notion of truth and the universe relate to each other - are the frameworks we build actual descriptions of the universe, with a singular truth binding potential statements, the frameworks to which they are relative, and the universe itself into judgement, or do we divide our frameworks in theory from the universe, considering them different in nature and not fully matchable? If we were to be as conservative as above, the answer would be that it does not matter, although I do not take that stance on this issue. Also unique to this situation is that it is the first step in our framework where actual data enters play (inconvenient because we are deciding what data can in principle mean). I hold that the answer to this is no in principle - our frameworks that would describe the universe are mediated by our senses and the shape of our potential thinking, and such thoughts cannot, both for lack of a method (to know that there is a real correlation) and, because our minds are not capable of the diversity of patterns and logics potentially in reality itself (presuming it's even sensible to talk about them that way). Instead, we consider our frameworks as structures attempting to capture what regularities in the universe as we can see through our senses (themselves corrected as best as we can), stated as clearly and powerfully as we can. We birurcate our notion of truth, considering statements true to the degree that they corrispond to our best (or a given, under certain circumstances, e.g. Newton's laws being pragmatically useful) frameworks, and consider those frameworks to be true to the extent that they capture regularities in the universe in ways conformant with whatever systems of judgement we have for their particular area of concern.
Our final classic deep foundational concern is theory of mind - is our mental self derived from the apparent properties of us as an object and do others have a mental life like ours? Developmentally, most people come to an effectively biological framework for this in infancy - while these frameworks may differ (either initially or as they further develop), they are functionally constrained to be within certain bounds. A philosophical reexamination of last prerequiste for both functional living and value philosophy requires a conclusion on this matter - without a notion of other people with a rich mental life, other-centric values are constrained to be at most hollow (e.g. if we wish to lessen the pain the suffering caused to others reflects into our emotions by our biological capacity for empathy) in their philosophical basis. Similarly, the nature of the us as beings is foundational (but more contentious) - if we view harms or pleasures brought on others as on something disconnected from the real them (that is, believe there to be a strong mind-body divide), we weigh these acts with a different seriousness and concieve of their fragility differently than if we see them as being entirely contained in their body. We are aided in our framework decisions at this level by a lot of information provided by modern science (scientific information is itself uncertain on several levels, from the foundations and methods to specific studies, but it still has proven in its many forms to be better than alternatives) - we have studies, thought experiments, and individual cases of the effects of brain damage to help us come to a reasonable conclusion that the naïve concept of the mind is a mystification of the function of the brain, that our subjective experience is a product of our brain, that physical damage to various parts of the brain limit its functions in ways appropriate to the region, that others have brains similar to ours, and that they have subjective experiences similar to ours (we are not yet required to take a stance on the nature of subjectivity, merely to note it).
These steps having been made, we have constructed some useful frameworks with a certain amount of tenativity, each (largely) relying on the ground provided by its predecessor, and each acting as a ground (both alone and in partnership with other levels) for later development. In our life as a thinker, we may decide to reshape some of these or to experiment with more than one competing framework. Many later frameworks, not being exclusive, are sharable without hedging (e.g. we might easily hold multiple definitions of justice to be distinct and relevant in our framework, or have varying notions of what constitutes valid evidence). By acknowledging our epistemology's areas of uncertainty, we avoid the intellectual dishonesty of styles of philosophy that would claim binary certainty and remain comfortable examining the metaphilosophic intuitions that guide us in the laying of these foundations. By concieving of these as layers that both make later thought possible and cost us certainty, we remain open to holding potentially many of these competing frameworks as alternatives to whatever one or few of them we use in our main perspective, giving us a greater ability to reshape our philosophy by having "seen through many eyes at once".