Had arrived, it would clearly be seen (6,2)

'seen' is the definition.
The answer and definition can be both to do with perception as well as being past participle verbs.
Maybe there's a link between them I don't understand?

'had arrived it would clearly' is the wordplay.
I cannot really understand how this works, but
'had' could be 'd' (in contractions e.g. 'I'd', 'you'd' etc) and 'd' is found within the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
The remaining letters 'showup' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'be' is the link.

Can you help me to learn more?