In 'Mental Events' Davidson wrote "...mental events are mental only as described". Many have taken this and other of his remarks as showing that he holds that the anomalousness and irreducibility of the mental is conceptual only. But to me this opens up a further mystery: if basic ontology is physical, how is it possible for there to be relations among concepts which cannot be physically mirrored
You touch an open question.
An ontology which includes only physical object will not suffice. At least one has to add entities from informatics centered around the concepts of information and information processing. Because mental processes can be considered information processing: The input results from our sensory organs, the processing employs in addition the actual internal state as a kind of memory. And the output are the actions of the system. Hence one needs a combination of informatics and physics necessary for the physical substrate of informatics.
To investigate the third person view of the mental and to capture it in a neuronal model is the subject of neuroscience. Here already intelligent and autonomous robots have been built, e.g., the rover on the planet Mars.
But qualia and the first person view are quite another issue.
Wehler is right. As your question is phrased, an exclusively physicalist ontology will not suffice (without deploying something like Wehler’s informatics ontology, or Klocking’s notion that concepts are emergent properties of [some] physical entities). But the ontological issue issue is alive and well, as you can see from nir/wehler’s lively discussion (with no end in site).
Start by considering the “knowledge argument,” which purports to show that physicalism is wrong because conscious experience involves non-physical properties, and is premised on the idea that someone who has “complete physical knowledge about another conscious being might yet lack knowledge about how it feels to have the experiences of that being”. See http:plato.stanford.edu/entries/qualia-knowledge/ for a full rendition of the notion and issues. Here, you will find Frank Jackson’s formulation of the idea which underlies the knowledge argument in the now famous example of the neurophysiologist Mary:
“Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like ‘red’, ‘blue’, and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal chords and expulsion of air from the lungs that results in the uttering of the sentence ‘The sky is blue’.… What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not? It seems just obvious that she will learn something about the world and our visual experience of it. But then is it inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism is false.
The argument contained in this passage may be put like this: (1) Mary has all the physical information concerning human color vision before her release. (2) But there is some information about human color vision that she does not have before her release. Therefore (3) Not all information is physical information”
Your specific point is addressed later, where it is pointed out that “talk of ‘physical information’ in the context of the knowledge argument is ambiguous between an epistemological and an ontological reading," and two alternatives are offered: The weaker, epistemological version:
(1a) Mary has complete physical knowledge concerning facts about human color vision before her release. (2a) But there is some kind of knowledge concerning facts about human color vision that she does not have before her release. Therefore (3a) There is some kind of knowledge concerning facts about human color vision that is non-physical knowledge.
And the stronger, ontological, version:
(1b) Mary knows all the physical facts concerning human color vision before her release. (2b) But there are some facts about human color vision that Mary does not know before her release. Therefore (3b) There are non-physical facts concerning human color vision.”
The ontological version is then made explicit as follows:
“Premise P1 Mary has complete physical knowledge about human color vision before her release.
Consequence C1 Mary knows all the physical facts about human color vision before her release.
Premise P2 There is some (kind of) knowledge concerning facts about human color vision that Mary does not have before her release.
Therefore (from (P2)):
Consequence C2 There are some facts about human color vision that Mary does not know before her release.
Therefore (from (C1) and (C2)):
Consequence C3 There are non-physical facts about human color vision.”
And the article goes on to outline the various ways that C3 (ergo dualism?) can be avoided, and is a fairly good primer on thinking about whether your “basic” premise, that “ontology is physical” is tenable.