In biology, most things are predictive: Toxicity is given in LD50, but one cannot know which half of the population will die, 1% of kids will be born with some type of autism, but we don't know which kids (obviously, there are risk factors, but nothing is absolute), etc....

On the other hand, if I combine water with an acid, it absolutely heats up. If I drop my coffee cup, it's absolutely falling to the floor. (A pedant might mention that the coffee cup doesn't fall in space, but that gets to the heart of the matter - there are preconditions that we understand in physics, but as sciences get softer, those preconditions become less well understood - I assume that as Biology matures, we will understand better those).

I need two words which emphasize the difference between A often causes or predicts B and A must cause B.

  • A law, as in the law of gravity, the law of thermodynamics*? Mar 23, 2017 at 17:00
  • Interesting thought! I'd prefer an adjective. I also don't really see laws as that absolute, especially because I definitely broke the law on my way to work this morning.
    – user121330
    Mar 23, 2017 at 17:04
  • 1
    you need a word that is more certain than law? Mar 23, 2017 at 17:10
  • 2
    @WeylandYutani I think "certain" is the appropriate adjective...
    – Laurel
    Mar 23, 2017 at 18:28
  • 2
    Also invariably. This contrasts rather well with a probability.
    – Xanne
    Mar 24, 2017 at 2:59

2 Answers 2


There are some good suggestions in the comments, which I'm going to pick from in my answer. All definitions from Merriam-Webster unless otherwise noted.

A guarantees B
Guarantee: an assurance for the fulfillment of a condition

A invariably causes B
Invariably: on every occasion

A makes B certain / A makes B certain to occur
Certain: (3a) dependable, reliable - (a certain remedy for the disease)
(3b) known or proved to be true : indisputable (it is certain that we exist)
(4a) inevitable (the certain advance of age)
(4b) incapable of failing : destined - used with a following infinitive (she is certain to do well)

A necessitates B
Necessitate: to make necessary, to force or compel

A is sufficient for B / A is a sufficient condition for B
Sufficient Condition: a state of affairs whose existence assures the existence of another state of affairs. Note: This is common wording amongst philosophers, mathematicians and logicians, but it could sound odd in other contexts.

B is necessary for A / B is a necessary condition for A
Necessary Condition: a proposition whose falsity assures the falsity of another. Note: This is common wording amongst philosophers, mathematicians and logicians, but it could sound odd in other contexts.

I can't think of many options for cases when the causal relationship is specifically probabilistic. Again, philosophers have a word for it:

A probabilifies B
Probabilify: to make probable, give probability to (Oxford Living Dictionaries)

  • I hadn't included "certain" initially as the you'd have to structure the sentence differently, but it felt like it ought to be included ... and so now is. Hat-Tip to @WeylandYutani. Jun 17, 2017 at 15:02
  • Also a Hat-Tip to @Xanne for "invariably". Jun 17, 2017 at 15:03

A often causes or predicts B is theoretical, a premise.

  • theoretical - (adj) "based on theory."

  • premise (noun) "A proposition upon which an argument is based or from which a conclusion is drawn."

A must cause B is mathematical.

  • mathematical - (adj) "rigorously exact, precise, certain."
  • Theory is far more certain than hypothesis or even Truth to scientists. Interesting suggestions though...
    – user121330
    Jun 19, 2017 at 1:05

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