In the sentence,
"But that's not true."
I see a translation as
"Но это не правда."
I know 'правда' is feminine so it seems that the 'это' being used is the indeclinable particle, and not the adjective (or else, if the translation is correct, it would have used 'эта for the nominative case).
How can one tell/know which word to use - the indeclinable particle, or the declinable special adjective?
I know this is older, but I think this ties in well with the original question... How do you determine the subject, or object, of some difficult sentences, e.g. this question sentence. For instance,
'Чьи это вещи?' (Here это is indeclinable particle) or
'Чьи эти вещи?'
What do each mean? Which words are the subject? Which are the object?