[2] His role as a senior lawman makes it likely that he spent some time in his early life at a native Scottish law school, but this is simply reasoned conjecture.
[9] In this role, he appears alongside the Judex Máel Domnaich mac Meic Bethad (Maldoven son of Macbeth) as arbitrator in a land dispute between a knight called Robert of Burgon (aka Robert the Burgundian, who owned the estate of Lochore, which bordered the disputed territory), and the Céli Dé of St Serf's Inch.
In this case, both Causantín and Máel Domnaich chose to defer to the superior legal wisdom of another Judex, Dubgall mac Mocche (Dufgal son of Mochta(?)).
[10] Causantín appears in a charter of King David's, dated 1126, giving confirmation of the rights of Dunfermline Priory and promoting it to Abbey status.
His name occurs as a witness, alongside bishops John of Glasgow, Robert of St Andrews, Cormac of Dunkeld, Gregoir of Moray, Mac Bethad of Rosemarkie, and mormaers Máel Ísu of Strathearn, Ruadrí of Mar, Matad of Atholl, as well as his kinsman, Gille Míchéil, chief of Clann meic Duib and others.