One of the often-repeated arguments against the theory of conjectural knowledge can be called the argument from technology.
Mises: “The popular prestige that the natural sciences enjoy in our civilization is, of course, not founded upon the merely negative condition that their theorems have not been refuted. There is, apart from the outcome of laboratory experiments, the fact that the machines and all other implements constructed in accordance with the teachings of science run in the way anticipated on the ground of these teachings. The electricity-driven motors and engines provide a confirmation of the theories of electricity upon which their production and operation were founded. Sitting in a room that is lighted by electric bulbs, equipped with a telephone, cooled by an electric fan, and cleaned by a vacuum cleaner, the philosopher as well as the layman cannot help admitting that there may be something more in the theories of electricity than that up to now they have not been refuted by an experiment.”
That line of argument is really not worthy of a serious scholar. To observe the instrumental value of theories does not to refute the theory of conjectural knowledge. The instrumental use of a theory does not represent a confirmation of the theory. The Ptolemaic system could be used for a lot of practical applications. It just means that the theory is near enough for practical purposes.
That was posted previously http://www.criticalrationalism.net/2010/03/08/mises-and-gordon-on-popper/
Blackburn: “It is all very well saying that it is a bold unfalsified conjecture that my GPS will tell me where I am. But unless it is a bold conjecture that I can rely on, that give me no reason to spend any money on it. I do not want it to be a bold conjecture that my flight will life off and answer to the controls. I want it to be a racing certainty. For that we need our confidence to match what happens. That is the gold standard, for knowledge and truth alike.”
http://www.criticalrationalism.net/2010/07/12/simon-blackburn-on-popper-from-the-sidelines/
Comments:
On Mises. The theory of conjectural knowledge does not preclude the practical application of laws that are known to be false but are well tested and are (a) the best we have at present, and more important (b) known to work well enough under the situations and circumstances where the machines and appliances will be used.
On Blackburn. Similar rejoinder applicable. In addition, we need to examine more closely the reason we may buy a GPS system or confidently board an aeroplane.
On the GPS, it would appear that Blackburn has never been in a situation where the GPS did not work! No doubt early systems were much less reliable than the current versions on the market, this is not a result of faith in something or other but a result of error elimination during development and then testing in the marketplace.
On the performance and safety of planes, I suspect that our confidence is not based all that much on belief in the laws of nature but more on the Popperian process of testing and and error-elimination by the ground staff who service the machine and try to ensure that there are no defective parts in place before takeoff. Planes still crash, sometimes because of defective service. Nervous travellers make a point of checking the comparative safety records of the airlines.
Conclusion. What has the argument from technology got to do with the status of deep (fundamental) explanatory theories which are contested at the frontier of knowledge?
We can and do create successively better (truer) ideas. Popper had no problem with truth. One of his claims was that fallibility and truth are not enemies. So to criticize him on the basis “look around us — knowledge really works — we have found some amount of truth” … that just misses the point.
The real issue is: how do we find truth? Is it by fallibilism and criticism, or by support and justification? Both of these are methods of learning, but the difference is the first one actually works.