Explain with the two-tier discipline.

The fact — the thing, the state, the relation: the existent (or non-existent) that the senses perceive — the physical facts (the act, the object, the place) and the psychological (the intention, the knowledge, the motive). The proof's classic pair: the factum probandum (the fact to be proved — the issue) and the factum probans (the fact proving — the evidence). Fact in law vs. fact in issue: The fact in law — the facts with legal consequence in the abstract: the law's raw material (any fact the law attaches effects to); The fact in issue — the facts this case's outcome depends on: the material facts as defined by the pleadings (the civil) or the charge (the criminal) — the elements of the cause of action or the offence (the contract's offer-and-acceptance; the crime's actus reus and mens rea). The distinction's work: not every fact matters — only the facts in issue (and the relevant facts serving them) are the trial's business.