Full Idea
'Every event has a cause' and 'truth is correspondence to facts' are candidates for being synthetic a priori knowledge.
Clarification
'Synthetic a priori' is 'known to be a fact about reality just by thinking'
Gist of Idea
Maybe our knowledge of truth and causation is synthetic a priori
Source
Roger Scruton (Modern Philosophy:introduction and survey [1994], 13.2)
Book Reference
Scruton,Roger: 'Modern Philosophy: introduction and survey' [Sinclair-Stevenson 1994], p.162