I often find that Donald McLeod illuminates a tricky theological question with uncommon clarity and insight. 

Here’s what the Professor has to say about what we call ‘chance’ or ‘accident’ in the light of God’s fore-ordination:-

God’s fore-ordination does not eliminate contingency. It does not rule out what we call chance or accident. Very often we hear good and pious people saying there is no such thing as chance or accident. Our Confessions do not agree with that. The Westminster Confession tells us that fore-ordination does not take away the liberty or contingency of second causes (111:1). When we say that some things are contingent, that they occur by chance, that they are accidents, we do not mean that they are not foreseen by God or not covered by His fore-ordination. What we mean is that they are, in principle, unpredictable so far as we humans are concerned. In other words, supposing we knew all the facts and could gather them all into our own statistical calculations, there are still certain events which are contingent and accidental and inherently unpredictable. This is not simply a matter of the limitations of our human powers of observation. Physicists tell us there is a principle of uncertainty at the very heart of the physical universe. It is in principle impossible for us to predict simultaneously both where the primary particles of mass and energy are and where they are going. We can predict the behaviour of large masses (quanta) of particles but not the behaviour of individual particles. The same is true, at a more mundane level, of the fall of the dice. Such an event is in principle contingent so far as our human observation is concerned, and divine fore-ordination does not eliminate that fact. It is a very interesting question how the behaviour of atomic particles relates to God’s fore-ordination, but the position that there are in our physical universe particles which behave contingently and unpredictably seems clearly established. God has fore-ordained that they behave randomly.

A Faith to Live By