As explained in the introduction, the relation I am calling “token causation” is a relation between two actually occurring, concrete, token events, while type-level causation relates abstract entities called “properties,” “types,” or “factors.” In the preceding chapters, I used upper case italicized letters to represent factors. Now we need to refer to token events, and I will use lower case italicized letters, x, y, z, and so on, for this purpose. As explained more fully below, the relation I wish to analyze in this chapter, in terms of probability relations, is roughly this (where x is of type X and y is of type Y): x's being of type X caused (atemporally) y's being of type Y. Another way of putting it is as follows. Where x takes place at time and place <tx,sx> and y takes place at time and place <ty,sy>, the relation I wish to analyze is this: things’ being X at <tx,sx caused things to be Y at <ty, sy.

The basic idea in the probabilistic theory of type level causation was that causes raise the probability of their effects. We saw that this idea needed several qualifications. The possibilities of spurious correlation and causal interaction had to be accommodated, and it was necessary to build into the theory the requirement that causes precede their effects in time.