Which conditional is this?
If John did not come to work yesterday, he was probably ill.
I would hazard a guess that it is a first conditional as there is a fair probability that John being ill was actually the reason for not coming to work - however, all the references I have indicate that the first conditional is for the future only.
Thanks for any comments / explanations!
If John did not come to work yesterday, he was probably ill.
This isn't any of the conditionals you mention. It is not an example of one statement depending on another; it is a statement of logic that one thing must mean another.
The speaker is indicating that he does not know for certain whether John came into work or not - but if it is true that he didn't, that would probably be because he was ill.
Consider what the same person might say if they knew for certain that John did not come into work, but was still unaware of his reason:
John did not come into work yesterday. He must have been ill.
If he was aware of the absence and the reason, he would probably say:
John didn't come into work yesterday because he was ill.
The "First, second, third conditionals" are lies told to children. They help to give some structure to learning the conditional structures in English, but don't give every possible combination of tenses.
Here it is clear that the condition is "real". It is factual so this functions like a "zero conditional". It expresses an implication, rather than a prediction.
