(C1) **SOF causes Step**;
(O1) Step →IS−A Evolution, (O2) Slow increase →IS−A **Evolution** (O3) Sharp step →IS−A **Step**.

Here are the explanation atoms which can be derived:
(E1) SOF *explains* **Step** bec *poss*{SOF}, (E2) SOF *explains* **Evolution** bec *poss*{SOF}, (E3) SOF *explains* Sharp **step** bec *poss*{SOF, Sharp **step**}.

Let us consider Point 1 above: Our concern here is about SOF *explains* Sharp **step** bec *poss*{SOF, Sharp step} **which can be inferred**
versus SOF *explains* Slow **increase** bec *poss*{SOF, Slow increase} **which cannot.**
Why is it sensible to explain "evolution" and "sharp step" by a "sliding of the flywheel" while "slow increase" could not be explained by the same "sliding of the flywheel"? The reason is that, from the facts given here, a "slow increase" is not a "step" (which is indeed explained by some "sliding of the flywheel"), but another kind of "evolution". So, explaining "slow increase" by some "sliding of the flywheel" would be unmotivated from what we know about the system. On the other hand, it is possible that some "sharp step", which is a kind of "step", has been provoked by some "sliding of the flywheel". Notice that if there were reasons to eliminate this possibility, it should have been noticed. We could e.g.

have added the information ¬(SOF ∧ Sharp step) in W**. Another way would** be to replace C**1 by (**C1
′) SOF causes Moderate **step**,
and to modify the ontological information accordingly.

This example also shows that we must exercise some care while stating the ontological information, which was to be expected since the ontological information plays a great rˆole in the formalism. Since a "step" is an "evolution", there are good reasons to explain "evolution" also by some "sliding of the flywheel": If we have enough information to know that we get "evolution", but **not enough**
to know whether it is a "step" or not, it is natural to provide "SOF" as an explanation for this "evolution".

Let us consider Point 2 now. For this purpose, let us add the following information about the system: "Any *evolution* **in the vibration measurement** signal causes an *alarm* **to be displayed on the operator control screen."**
We would then add the following formula to our causal theory.

(C2) **Evolution causes Alarm**. The theory is now described by C1, C2 together with O1, O2 and O3 (W
does not contain special information, only the consequences of these formulas).

Then, the explanation atoms derived by the new theory are E1, E2, E3 and E**4, plus** E2
′ obtained by transitivity from E2 and E**4 and by an obvious**
simplification, with E**4 and** E2
′ **as follows:**
(E4) **Evolution** *explains* **Alarm** bec *poss*{**Evolution**},
(E2
′) SOF *explains* **Alarm** bec *poss*{SOF}.