Design continued: A tale of two knives
The other is a stone knife, or seems to be, made from chert around 6,000 years ago.
What can we infer about the objects? Well, it may seem obvious that they both are made by design or intent. But it is possible that a suitably primitive stone knife is indistinguishable from an accidental flake of chert caused by another falling rock hitting a cliff face. There is no seemingly plausible account of the Toledo sword being made by unintentional processes.
Why can we reliably infer design in the case of the sword and not the stone knife? Let us consider some reasons:
1. We have a historical record of Toledo blades, but not of stone knives. Well, yes, this is true, but if we came across one for the first time, with no prior record or knowledge or Toledo blades, Damascene steel, or even human warfare, we'd likely conlude it was made by technologically sophisticated manufacturers, and that it was designed to do its job - either by the sword maker or by a tradition of sword making to which the maker was heir. It doesn't matter if the designer is a single individual or a tradition here.
2. The complexity of the structure is not producible by any known natural (i.e., non-artificial) process, while it is known to be the sort of thing humans make. Complexity alone is not sufficient as an indicator of design, despite the assertions of the IDevotees. Many natural things are complex (in particular, the microstructure of minerals and crystals). But as we uncover more about the natural world, we get an increasingly clearer idea of what the natural world can produce, and very surprising it is too. The usual argument for ID is based on an argument from incredulity, as Dawkins calls it, or a failure of imagination.
3. We know the function of swords in human culture. We also know the function of stones with sharp edges, but unless there is some sort of complexity (flaking patterns on the edges) that could only feasibly be produced by humans, we can't tell if it is a natural or an artificial product.
Are you starting to see a pattern here? We can tell if it is designed only if we know the sorts (classes) of things that designers produce, and the classes of things produced in the natural world without design, and the instance in question is in one but not the other.