The four familiar categories
Most American fault law fits into one of four categories: pure comparative negligence (recovery reduced at any fault level, never barred), modified comparative negligence with a 50% bar, modified comparative negligence with a 51% bar, and pure contributory negligence (any fault at all bars recovery).
Why South Dakota genuinely doesn't fit
South Dakota's slight/gross negligence standard, under SDCL § 20-9-2, asks a fundamentally different kind of question than any of these four categories. Rather than comparing the plaintiff's fault to a fixed percentage threshold, it asks whether the plaintiff's own negligence was qualitatively "slight" compared to the defendant's "gross" negligence. This makes South Dakota a genuine fifth category, distinct from the pure/modified framework that governs the rest of the country.
Where it lands relative to the other four
In practice, South Dakota's standard is stricter than even a 51% bar state: a real case, Wood v. City of Crooks, held that 30% fault was "more than slight," barring recovery entirely — a result that would be unthinkable in a 51% bar state, where 30% fault would still mean recovering 70% of damages. At the same time, it's more forgiving than pure contributory negligence, since some genuinely slight fault (generally in the 10-20% range, based on case patterns) does still permit a reduced recovery rather than barring it outright.
Why this genuinely matters when comparing states
Someone researching how South Dakota's negligence rule compares to a neighboring state can't simply look for a percentage threshold the way they could between two 51%-bar states, or between a 50% and 51% state. The comparison has to account for South Dakota's qualitative "slight" standard, which behaves meaningfully differently from any percentage-based rule. See our guide to why no other state shares this rule for more on just how isolated South Dakota's approach is nationally.