???"Exorbitant" foreign laws that impose citizenship on Australians "willy nilly" and without their knowledge should not disqualify them from Parliament, lawyers for Deputy Prime Minister Barnaby Joyce have argued in the High Court.
On the first day of hearings into the "citizenship seven", Bret Walker SC - who is also representing deputy Nationals leader Fiona Nash - said section 44 of the constitution was aimed at avoiding split allegiance among MPs.
"There's no split allegiance where you're not aware of one of them," Mr Walker said. "You cannot heed a call you cannot hear."
Mr Walker said "exorbitant" foreign laws that imposed citizenship by descent - often without the knowledge of those affected - could not be seen to create any split allegiance. He maintained that Mr Joyce and Senator Nash did not know about their dual citizenship.
Mr Joyce discovered in August he was a dual citizen of New Zealand because his father was born there. Senator Nash later realised she was a British dual national.
"It is highly significant that no one suggests section 44 - in its historical provenance - had as its aim the prevention of people having willy nilly or unwittingly been given citizenship by descent," Mr Walker told the court.
Solicitor-General Stephen Donaghue, appearing on behalf of the Turnbull government, said that to disqualify Mr Joyce, Senator Nash and three others - Nationals senator Matt Canavan, former Greens senator Larissa Waters and crossbencher Nick Xenophon - would go against the "operational purpose" of section 44, because none of them knew about their foreign ties.
All five were born in Australia, except for Ms Waters who was born in Canada to Australian parents. Mr Donaghue argued there should be a distinction between these sorts of "natural-born" Australians and overseas-born "naturalised" Australians.
One Nation senator Malcolm Roberts and former Greens senator Scott Ludlam - who were born in India and New Zealand respectively, to at least one foreign parent - were in the latter category.
The government believes Senator Roberts and Mr Ludlam - who along with Ms Waters has already quit Parliament due to dual-citizenship - should be ruled ineligible because they were born overseas, came to Australia later in life and should have been aware of the real prospect of foreign citizenship.
Mr Donaghue argued that if any parliamentarian had - or should have had - knowledge of their status "and they shut their eyes to it" then they should be found in breach. This is the test he said applied to Senator Roberts and Mr Ludlam.
Tracing the history of section 44 back to British and colonial law, Mr Donaghue argued there had always been a distinction made between natural-born and naturalised citizens in the past.
Only parliamentarians who have "voluntarily obtained or retained" should fall foul of section 44, he said.
The Solicitor-General conceded the Commonwealth was asking the court to take a "narrower" view of section 44 than it had previously, most notably in the 1992 case of Sykes v Cleary.
However lawyers for Ms Waters and Mr Ludlam will call for a more literal reading of section 44, arguing ignorance is no defence.
The hearings are expected to continue until Thursday.
- This story first appeared at The Sydney Morning Herald.