Relevance and Its Limits
Core concepts
Relevance is the threshold of admissibility: evidence is relevant if it has a tendency to make a fact of consequence more or less probable than it would be without the evidence. Relevance is relational - it depends on the issues framed by the pleadings and the applicable substantive law - and it is assessed by logic, not by weight. Learn the two-step analysis: logical relevance, then the discretionary or mandatory exclusion under the probative-versus-prejudice balance. Unfair prejudice, confusion of issues, misleading the tribunal, undue delay, and wasting time are the classic counterweights.
Know the categorical limits that operate even on relevant evidence: subsequent remedial measures, offers to settle, payment of medical expenses, and liability insurance are excluded when offered to prove fault or liability, but admissible for impeachment or other limited purposes. Character evidence is the other major limit: in criminal cases the prosecution may not lead propensity evidence about the accused, subject to the door-opening exception when the accused introduces character or reputation; evidence of prior bad acts may come in for non-propensity purposes such as motive, intent, identity, absence of mistake, or plan.
Traps
Questions often supply evidence that is logically relevant but offered for an impermissible purpose. Watch for the difference between propensity use and non-propensity use, and for the requirement of a limiting instruction. Do not treat all prejudicial evidence as inadmissible - all probative evidence is prejudicial; only unfair prejudice counts.
Worked example
After a fall, a shop repairs its staircase. The repair is relevant to show the staircase was defective, but it is excluded when offered to prove negligence. It may be admitted, however, to impeach the shopkeeper who testifies the stair was always sound.
Rule of thumb
Ask first "does it tend to prove a fact of consequence?", then "is it barred by a categorical rule or outweighed by unfair prejudice?"