[SystemSafety] The States and Modes debate

[Paulo Carvalho]

Hello gents,

pardon my intromission, but I see the INCOSE Systems Engineering Handbook
as a domain agnostic reference/guideline, and in that sense would see
reasonable that text distinguishes between "state" and "mode" even if not
providing a definitive definition for each.

Thus, leaving the user to define those terms for the particular
/application/domain/system they are working on.

I could see a situation where a system has different operating *modes
*(nominal,
degraded, power-off, etc.) and each of these modes includes
different internal *states. *
Cheers
Paulo



On Fri, May 22, 2026 at 10:19 AM Prof. Dr. Peter Bernard Ladkin <
ladkin at causalis.com> wrote:

> On 2026-05-22 01:27 , Les Chambers wrote:
> >
> > In these contexts, synonyms abominate the functional Safety countryside.
> They must be hunted down
> > and eliminated with extreme prejudice - along with the “qualitative
> state machine(s)” they rode in
> > on.
> >
> First, it seems silly to me to renounce synonyms. In the 61508 context, it
> would be ridiculous to
> insist people say/write Equipment Under Control when they can write EUC
> and even more ridiculous to
> insist they say/write Equipment Under Control Control System when they can
> say/write EUCCS.
>
> Second, you seem to have a prejudice for working with numbers when it
> comes to state machines.
> That's fine, I guess, as a personal preference. But if you perform any
> system development using
> formal methods (which 61508 now says is "highly recommended" for any
> safety function) you will very
> quickly have to get used to manipulating state machines which work on
> symbols which are not numbers.
> For almost all formal verification techniques for the last 57 years use
> them or some equivalent.
>
> PBL
>
> Prof. Dr. Peter Bernard Ladkin
> Causalis Limited/Causalis IngenieurGmbH, Bielefeld, Germany
> Tel: +49 (0)521 3 29 31 00
>
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