‘Proposition’ is a cover term for the meaning of a clause minus its basic illocution. Now a distinction applies to these objects by the criterion of whether the situation that they represent is located in space and time. Consider and .
| . | The earth is a planet of the sun. |
| . | The earth revolves around the sun. |
may be situated in space and time, e.g. by adding between 9.21 and 21.71 billions of years after the big bang. What is designated by this sentence is observable. On the other hand, cannot be provided by spatio-temporal coordinates. If it can be said to be observable, this is only an inference based on an observation of . The meaning of is a thought, while the meaning of is a state of affairs.
In Lyons's (1977, ch. 11.3) ontology of naïve realism, a state of affairs is a second-order entity, while a thought is a third-order entity. In the terminology used here, the meaning of the clause of both and is a proposition; but the former is a thought, the latter is a state of affairs.
Certain predicates like ‘believe’ () and ‘say’ (e.g. Latin dicere) take a thought as their object. In this, they differ from other predicates, e.g., perception verbs like hear (), which take a state of affairs as their object. and share the proposition that the defendant braked before the collision.
| . | The witness believes that the defendant braked before the collision. |
| . | The witness heard the defendant brake before the collision. |
As two further examples, the complement clause of designates a thought; the complement clause of designates a state-of-affairs.
| . | I know that Jim took his coat. |
| . | I saw Jim take his coat. |
The difference between the two ontological statuses of what is designated by a complement clause depends partly on the matrix verb whose argument the dependent clause is: Propositional attitudes like ‘believe’ and ‘know’ are directed towards thoughts, while perceptions like ‘hear’ and ‘see’ are directed towards states of affairs. Some of the relevant semantic distinctions are summarized in the following table:
| property | thought | state-of-affairs |
|---|---|---|
| mode of existence | 'exist' | 'occur, 'take place', 'happen', 'obtain' |
| locus | in the mind | in a possible world |
| located in space and time | no | yes |
| directly sensorily perceptible | no | yes |
| matrix predicates | 'know', 'believe', 'assert', 'deny', 'remember', 'forget' ... | 'see', 'hear' ... |
| can contain negation | yes | no |
| applicable modal attributes | true, false | (un-)real, (im-)possible, (im-)probable ... |
The distinctive features of the table may be summarized by saying that a thought is thinkable, while a state of affairs is observable.
Occasionally, there is a structural difference between complements coding a thought and complements coding a state of affairs. In English, a complement clause coding a thought is generally a that-clause, while a complement clause coding a state of affairs is commonly non-finite. This appears already from a comparison of and . Compare again with .
| . | The witness heard that the defendant braked before the collision. |
indicates an immediate perception of the witness in the collision situation; he heard the braking sound. In typical uses, does not mean this. Instead, it means that the witness heard something which makes him believe that the defendant braked. This shows that the interpretation of a complement clause as representing or not a state of affairs does not depend exclusively on its matrix predicate. It may also be coded by the internal structure of the complement clause.
A state of affairs can be realized in a certain manner. In linguistic coding, this is taken for granted for many kinds of states of affairs. This is the basis of the ambiguity ilustrated by (Katz & Postal 1964: 123f).
| . | I dislike John's driving. |
is ambiguous because the object of the antipathy may be either the fact or the manner of John's driving. This is, again, a peculiarity of states of affairs not shared with thoughts.