Deductive mood

The deductive mood is an epistemic grammatical mood that indicates that the truth of the statement was deduced from other information, rather than being directly known.[1] In English, deductive mood is often indicated by the word must, which is also used for many other purposes. By contrast, some other languages have special words or verb affixes to indicate deductive mood specifically.

An example in English:
There's gas in the house! Someone must have left the stove on!
(deductive indicated by must)

References

  1. ^ Loos, Eugene E.; Susan Anderson; Dwight H. Day, Jr.; Paul C. Jordan; J. Douglas Wingate. "What is deductive mood?". Glossary of linguistic terms. SIL International. http://www.sil.org/linguistics/GlossaryOflinguisticTerms/WhatIsDeductiveMood.htm. Retrieved 2009-12-28. 
what is expressed
objectively: Realis
what is expressed
subjectively: Irrealis
what is logical: Alethic
 
what should be: Deontic
promises, threats: Commissive
 
commands, requests,
requirements: Directive
hopes, wishes, fears: Volitive
what would be:
Conditional (Eventive)
 
what may be: Epistemic
inferences, possibilities,
questions, etc.