LSAT Not-Laws: The Logic Games Deduction Technique Most Students Miss

A not-law (also called a negative inference or "not-arrow") records that a specific entity cannot occupy a specific slot. On your diagram, you write the entity's letter beneath a slot with an X or a strikethrough: "A cannot go in slot 3."

Not-laws are not rules given directly in the setup. They are deductions you derive from combining rules. The test writers do not tell you "A cannot go in slot 3" — you figure it out, and that figuring is worth several points.

Most students note positive placements (A must go here) and conditional rules (if B is in slot 2, then C is after D). Not-laws are the third pillar of a complete setup, and students who skip them routinely stall on the hardest questions.

Consider a 5-slot linear game with the rule "A comes before B." This rule eliminates specific slots for each entity:

A cannot be in slot 5. (If A were in slot 5, B would have nowhere to go after it.)

B cannot be in slot 1. (If B were in slot 1, A would have nowhere to go before it.)

These are the minimal not-laws from this rule alone. Add more constraints and the not-laws compound.

Rule: "A comes before B, and B comes before C." Now:

A cannot be in slots 4 or 5.

B cannot be in slots 1 or 5.

C cannot be in slots 1 or 2.

You derive these by asking: "How many entities must come before (or after) this one?" The answer tells you how many slots are unavailable at the beginning or end of the sequence.

In an in-out grouping game, a rule like "If A is selected, then B is not selected" immediately generates a not-law: if you're building the in-group, A and B cannot both be in.

A biconditional rule "A is in if and only if B is in" means A-without-B and B-without-A are both impossible. Mark both not-laws on your in-group list.

In a game where entities are placed into two teams, "A and B cannot be on the same team" eliminates A and B from sharing any slot in either team column — a not-law for each possible pairing in that dimension.

Conditional rules often generate not-laws through their contrapositives. "If A is in slot 1, then C is in slot 3" means: if C is NOT in slot 3, then A is NOT in slot 1. This gives you a conditional not-law: ¬C3 → ¬A1.

When that conditional fires (and you know C is not in slot 3), you immediately write A's not-law on your diagram: A ✗ slot 1.

The habit: whenever you derive a contrapositive, ask yourself whether that contrapositive produces a not-law for any specific slot. If yes, write it immediately.

Write not-laws below your main row of slots — a second row where each slot has an X for any entity that cannot go there.

Some students use a separate "not-law table" listing each entity and its forbidden slots. Either method works; the key is that not-laws are visible when you scan the diagram, not buried in your notes.

Not-laws are especially valuable when a question asks "which of the following could be true?" You eliminate choices immediately if they place an entity in a slot you've marked with a not-law. No case-testing required.

Games that feel unsolvable at first often crack open once you build your full not-law list. Not-laws constrain your valid arrangements more than students expect. When a slot has four entities that can't go there, only one or two remain — and the game becomes nearly determined.

The best use of not-laws is on "must be true" questions. If an entity has only one slot available after all not-laws are applied, that entity must go in that slot. You found a definite placement without an if-condition — the hardest type of deduction — just by eliminating the impossible.

Verbloom's games practice shows feedback on your diagram, not just your answers. If you missed a not-law that would have unlocked a question, you'll see it flagged.