These words seem very difficult to translate into idiomatic Latin. 'Supposedly' is used to express doubt that something is what people say it is, e.g. 'The queen supposedly finds Meghan Markle a nightmare from the royal family’s point of view.'
Secondly, the phrase 'supposed to' is a difficult phrase to define. It can mean 'obliged to' or 'intended to' or 'to have a duty or responsibility to' or 'expected to'.
It is often used in the context of meetings or arrangements as 'I am supposed (exspecto dum + subjunctive doesn’t quite capture the meaning) to meet a certain Mr. Panayiotis here at 10 a.m.'
Examples of the various sentences in which this idiom is used are (from the Cambridge English Dictionary):-
- What are you doing out of bed - you're supposed to be asleep?
- The whole conference was totally disorganized - nobody knew what they were supposed to be doing.
- The appointments are supposed to be made without fear or favour.
- You know full well that you're not supposed to go there without asking me!
- You're supposed to put the handbrake on whenever you stop on a hill.
- I was supposed to be working this evening but what the hell - I'll see you in the pub in half an hour.
In the sense 'intended to' we say 'This LED torch battery is already broken: it was supposed to last for three years!'
Here it seems to mean 'am able':- 'How am I supposed to (= how can I) find that much money by the end of the week?'
Lastly, how would one say in Latin 'a supposed expert' in the sense that he is believed by many people to be so, but often doubted to be so by the person who is speaking or writing?
In some contexts existimatur could be used, or licet and debeo.
But how is 'I am supposed to meet her' to be translated into Latin?
Or a 'supposed expert'. In fact in the sense of 'so-called' it is very difficult to convey this sceptical or scornful nuance in Latin. ut dicunt is too neutral, as are most expressions I have found in Latin.
I have tried to sort out the various meanings of this idiom and I realise that my question is too general but if suggestions for one or two of the more tricky examples like 'supposedly' and 'supposed to meet' and 'a supposed expert' can be made, I shall be satisfied.