‘whereby’

‘What is needed is a system _____________ citizens can feel safe but not monitored.’

‘By which’ ‘In which’ and ‘through which’ ‘by means of which’ and ‘according to which’ would all be possible here.

All of these are synonyms for ‘whereby’.

‘Where’ could also be ok, but this usually refers to a place – ‘A place where citizens can feel safe’.

‘Whereby’ collocates with:

so it’s useful to use when you are suggesting solutions.

In the example above, it works well with the emphasis ‘What is needed is _________’.

Some examples:

What is needed is a frequent-shopper plan whereby customers earn discounts.
The government should introduce a scheme whereby you can buy now and pay later.
There is a proposal whereby EU citizens would be allowed to reside anywhere in the EU.

Take care

You can only use ‘whereby’ when the system is the OBJECT.

When the system (etc) is the SUBJECT, use ‘which’

e.g.

a system which helps the unemployed find work = a system whereby the unemployed are given help to find work.
a process which involves heating the water = a process whereby water is heated
a scheme which encourages people to recycle = a scheme whereby people are encouraged to recycle

whereby