Career highlights

People, Ideas and Events

I've been fortunate to work with some great people and have had some talented doctoral students. The latter include Gerd Wagner, Heinrich Wansing, and Levan Uridia.

One doesn't normally have good ideas very often, so it pays to exploit them to the full, if and when they come.

  • At the beginning of the 1980s it seemed like a good idea to use abstract logic and extensions of classical logic to formalise fragments of scientific theories. This was inspired by Veikko Rantala's work and I was fortunate that Veikko agreed to work with me to develop this into a theory of metascience that was quite novel at the time. This evolved into a book Roads to Commensurability that I wrote trying to show how translations could be established between the languages of rival formalised theories, thus highlighting their logical interrrelations.

  • In 1995 I finally solved a little problem that had been puzzling me for some time. I knew that the answer set semantics for logic programs must be related to an extension of Nelson's constructive logic with strong negation; but I didn't know which one. The pieces of the puzzle fell into place one day (after a short chat with Marcus Kracht) and I found I had invented or discovered (take your pick) a new system of reasoning that I called equilibrium logic. This created more scepticism than excitement at the time, but two brave colleagues, Agustín Valverde and later Pedro Cabalar, helped me develop this logic, study its properties and find ways to extend it with new functionalities. So nowadays it seems to be quite well accepted and there have been some excellent doctoral theses that have developed it further. So it's still alive and kicking today.

  • In 2001 I started to work again on intertheory relations, but now in the context of logic programs and theories in nonmonotonic logics. This time the inspiration came from Vladimir Lifschitz and we wrote a paper together with Agustín Valverde where we defined and characterised a relation called strong equivalence (see publications page). This started a new line of research in knowledge representation that is still active.

The best reward in science is praise from one's colleagues and peers, but it's also nice to receive official honours. I was very proud in 2014 to be elected EurAI (formerly ECCAI) Fellow.