Claim 3 is being supported by an argument provided by 4, 5, and 6. Of course, we might also ask what claims should be there to support 4, 5, and 6.
Theoretically, if all claims must be supported by reasons, then there would be no guaranteed starting points to any process of reasoning. In structural terms, every claim that we use at the top of a diagram would always appear to need a further argument above it to show why that claim was acceptable. In such a situation, reasoning would be impossible—the very ideas of 'foundations' would go out the window.
In practice it is much simpler. We take for granted that many, perhaps most, claims we use are not going to have explicit reasons, but instead will be presented as being 'self-evidently' acceptable (that is, without any evidence but themselves). Societies, and particular knowledge groups (such as a profession or academic discipline) within them, have many agreed conventions and assumptions that short-circuit the need to justify in detail every single claim they use; there are also many legitimate, accepted starting points provided by claims for which no further reasoning is required (because the argument for them exists implicitly in the surrounding context of knowledge and audience).
Now, strictly speaking, very few claims are logically self-evident. One that is, for example, would be the claim that 'Either you are pregnant or you are not'. No matter who this claim is applied to, no matter what the situation, it is self-evident. There is no category of a little bit pregnant'. But such claims are actually quite rare: their function in argument is simply to define a term in such a manner as to make clear its exclusivity. Such claims do not actually refer to the world, but to the words we use in the world—the claim 'My sister is pregnant' is not self-evident. However, many claims which are not self-evident are treated as if they are self-evident, revealing the social dimensions of reasoning. In the world of strict logic, outside of common practice and normal human interactions, virtually every claim must be supported by evidence; in the everyday world of reasoning, many claims are assumed to be self-evident. They must be regarded as such. There would be no
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