Fuzzy logic seemed like an active area of research in machine learning and data mining back when I was in grad school (early 2000s). Fuzzy inference systems, fuzzy c-means, fuzzy versions of the various neural network and support vector machine architectures were all being taught in grad courses and discussed in conferences.

Since I've started paying attention to ML again (~2013), Fuzzy Logic seems to have dropped off the map completely and its absence from the current ML landscape is conspicuous given all the AI hype.

Was this a case of a topic simply falling out of fashion, or was there a specific limitation of fuzzy logic and fuzzy inference that led to the topic being abandoned by researchers?

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    $\begingroup$ The words current, conspicuous, and hype in that one sentence answer the question. The AI hype is really singularity, technopoly, and deep learning hype masquerading as AI. Singularity ideas lack proof or even evidence. There is no POC for general intelligence including in humans -- watch the news -- and Google APIs don't exhibit intelligence using the pre-WWII definition of it. We've moved the goal to create the illusion of achievement. Deep learning is the programming 18th century mathematics into 21st century calculators, but it works as it should in business so everyone gets paid. $\endgroup$ – FelicityC Oct 26 '18 at 17:42

Fuzzy logic is not down trending. It's a common architecture selection for systems that require the representation of uncertainty in changing rules. The domains include work-flow control, aeronautics, chemical plant engineering, automated defense of cyber-attack, building systems, and business intelligence.

In natural language processing, it's up-trending under other names. Semantic nets are a logical structure with strengths assigned between nodes of the net based on meta rules, which is reminiscent of early fuzzy logic software.

For instance, the rule might be that a word that ends with -ly before a word associated with action may be an adverb modifying a verb in English, but it is not always the case. The rule's application is not smooth, meaning non-probabilistic. It is fuzzy.

There is no way to create a grammar for common speech or writing in any natural language. Language is dynamic and as practically non-deterministic as wind vectors. That's why grammar is a down-trending word among linguists and people working in NLP.

Cognition is expected to require fuzzy valuations to the black and white nature of early production systems developed at MIT, Cambridge, the U.S. Navy, Yale U, and other locations in Eurasia. People develop rules in their cortex and they rise and drop in probability when decisions are made after the rule seemed to have worked or didn't.

The logic that works to prove a math theorem may require discrete inference, but people are smart when they can weigh alternatives and apply rules in unique ways to partial data and limited experience.


Fuzzy logic itself is not bad, it is a good starting point for injecting expert knowledge into a pid control system. It is used in classical engineering lectures. Instead of describing a system only a by function like y=sin(x), the formula can be extended with sliding modes.

Fuzzy logic was used for approximate reasoning. It was the first attempt in modeling knowledge based systems. So called qualitative reasoning with fuzzy sets allows to utilize domain specific knowledge in an expert system. It was replaced by more sophisticated techniques like domain specific languages, ontologies and semantic networks which are more close to human knowledge.

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    $\begingroup$ Thank you for trying to accommodate non-English speakers! While English may not be the most commonly spoken language now, it is the official language of Stack Exchange (except on certain sites) - see also this SO blog post, especially the ending. I've therefore rolled back your edit. $\endgroup$ – Ben N Oct 26 '18 at 3:11
  • $\begingroup$ That English is everywhere and is accepted as a global lingua-franca is only true for the past. Nowadays the situation has changed and the people are preferring their own local language. Forcing somebody to learn English doesn't make much sense. $\endgroup$ – Manuel Rodriguez Oct 26 '18 at 6:03
  • $\begingroup$ @ManuelRodriguez That makes no sense. A lingua-franca is a common language people use to communicate. People using their own local languages has nothing to do with lingua-francas $\endgroup$ – Daniel Oct 26 '18 at 23:01

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