I am indebted to Father Duggan and Mr Griffiths for their comments on my letter.
I must first reiterate that I do not consider that in the evolution vs intelligent design debate, God's creation or sovereignty is in question.
In answering Mr Griffiths, irreducible complexity is a man-made concept. God's creation is indeed a mystery, but He need not have created according to our simplistic notions. Only now are we realising that there may be physical laws which actually mandate such construction, that for example, there are simple physical molecules which might, under extraordinary conditions, self-replicate into increasingly complex structures and feedback loops. What if the cell originated by the accretion and replication of such simple code bearing structures, so that what is complex, is not irreducible at all?
In answer to Fr Duggan, my reading of intelligent design means that there are certain macro (the human body) or microstructures (the cell) which are so irreducibly complex that they cannot be explained except by direct creation by the hand of God. Thus, intelligent design implies creationism, by excluding evolution.
I thank Fr Duggan for drawing attention to my criticism of the argument for cosmic intelligent design as allegedly developed by Aristotle and St Thomas Aquinas, and I find that this is indeed a common belief. My rereading - and that of others such as Armstrong - of Aristotle is that his notion was one of an immaterial but pantheistic prime mover far removed from cosmic design and creation.
As far as St Thomas is concerned, of the five ways, only the last could be interpreted as referring to design. But well-credentialled commentators such as Copleston SJ (arguably the greatest historian of philosophy) and Wippel do not see Thomas's fifth way (ST, SCG 1. c13) that way, as it seems to speak more to the providence of a final cause, than to cosmic design.
Indeed, Copleston in his Aquinas states that it would sit well with the hypothesis of evolution! At the very least, the argument from design is not heavily accentuated in Thomas, and it would appear that neither Aristotle nor St Thomas ever used the words intelligent design or cosmic designer. Intelligent design in particular is an entirely modern concept.
Since we will probably never know the mechanism of our origins, direct creation is clearly not untenable, but for modernity, the idea that evolution could have been the mode of God's creation makes perfect sense, and it is supported by a considerable body of evidence. However, intelligent design/creationism actually forbids God to create in certain ways which are offensive to some of His believers.