Blind Variation as Heuristics that May Fail?

December 23, 2020

Bruce Neilson and I have an ongoing discussion about our differing interpretation of Donald Campbell’s notion of “blindness”. Bruce has previously published a post explaining his interpretation of Campbell’s essays, and while I agree with much of what Bruce says, we have some important disagreements about what counts as “blind” and what doesn’t. To try to make some progress in this discussion, I’m going to respond to a part of Bruce’s essays that I disagree with. In particular, I’m responding to the section titled “Blind Variation = Heuristics that May Fail”.

Bruce says:

To Campbell, a computer program using heuristics in a deterministic way still counts as “blind” insofar as the heuristics might be wrong. Campbell states this view more explicitly in his discussion on computer algorithms used for knowledge-creation:

“For example, one of the heuristics used in Simon’s ‘Logic Theorist’ program is that any substitution or transformation which will increase the ‘similarity’ between a proposition and the desired outcome should be retained as a stem on which further variations are to be tried. Any transformation decreasing similarity should be discarded. …greatly reducing the total search space. It employs an already achieved [at a higher level in the nested hierarchy] partial truth. It produces computer search similar to human problem-solving in failing to discover roundabout solutions requiring initial decrease in similarity“


Here Campbell is using the concept of ‘blindness’ not in how the variations is selected but how they failed to have some selections available that might turn out to be useful later. This is, I believe, the true understanding of Campbell’s use of the term ‘blind variation.’

Bruce, I don’t really understand how you’re arriving at this interpretation. Could you elaborate? Campbell doesn’t mention the notion of “blindness” in the passage you quote at all, and I’m not sure why you interpret him as saying that the processes he’s describing are an example of blindness. He’s just describing how the logic theorist works, not claiming that the parts of the logic theorist he’s describing involve any blindness.

Just after the passage that you quote Campbell goes on to say “Beyond thus applying what is already known, albeit only a partial truth, the new discoveries must be produced by a blind generation of alternatives.” With this additional sentence in mind, my interpretation of this passage is that the process of reducing the total search space doesn’t involve blindness, but searching within the reduced space does. Campbell contrasts “applying what is already known”, i.e. reducing the search space according pre-established means, with making “new discoveries … by a blind generation of alternatives”, i.e. searching within the reduced space. It’s only the latter which he describes as “blind”.

Continuing from your article:

Campbell goes on to make this view even more clear:

“The ‘selectivity,’ [of Simon’s Logic Theorist program] in so far as it is appropriate, represents already achieved wisdom of a more general sort, and as such, selectivity does not in any sense explain an innovative solution. [i.e. it’s ‘blind’] Insofar as the selectivity is inappropriate, it limits areas of search in which a solution might be found, and rules out classes of possible solutions. Insofar as the selectivity represents a partial general truth, some unusual solutions are ruled out. Simon’s ‘heuristics’ are such partial truths…”


Heuristics created at a different level of the knowledge creation hierarchy that are then used at a lower level of the hierarchy are still considered ‘blind variation’ in Campbell’s theory even if we do not perceive them as such.

I don’t understand how you interpreted “selectivity does not in any sense explain an innovative solution” to mean “it’s ‘blind'”. Could you explain that in more detail? I also don’t understand why you emphasized the sentence that you did, I don’t see what it has to do with the point you’re making. He isn’t saying that the fact that the selectivity rules out classes of possible solutions makes it “blind”, he’s explaining the downside to using a selectivity mechanism in the way that the logic theorist does.

I don’t think that Campbell is saying that the selectivity is blind, it’s more like the opposite: he’s saying that the selectivity can’t explain why the logic theorist makes innovations, that can only be explained by the blind search within the narrowed-down space that’s left after the selectivity (which isn’t blind) has been applied.

Tags: Epistemology