There have been many achievements by symbolic approaches in AI.
Most of these are focused on the category ``systems that think rationally'' (as discussed in section 1.3.2) and are highly specialized. ``[M]ost well-structured problems such as textbook math and science problems, are simple because they tend to engage a constrained set of variables that behave in a predictable ways.'' [Ese06].
There are two types of intelligence: fluid or crystallized. Roughly, the former is categorized as the ability to learn or to solve problems, the latter is that which is learned.
General intelligence (Spearman's g-factor) is highly related to the fluid type of intelligence. Moreover, there is a strong neural basis for this relation. The general form of intelligence is highly influenced specifically by a frontal system [JD00].
"How strange that our most advanced systems can compete with human specialists, yet
be unable to do many things that seem easy to children."
Erik de Bruijn