Given a complex proposition of the form ‘S↴S as specified by ↴S’, then if ↴S specifies the manner in which S↴S is realized, it is a manner proposition, while if it specifies a circumstance which holds or does not hold besides the situation of S↴S, it is a circumstance proposition. A circumstance proposition specifies an independent situation, while a manner proposition specifies an aspect of S↴S. Manner clauses are traditionally called modal clauses. The term is, however, problematic since it suggests a connection with mood and modality which is not implied.

The distinction between manner and circumstance is more easily drawn for non-sentential adverbials: A manner is conceptually dependent on the main situation in that it could not occur without it. For instance, in , fast is a manner adverb, and it is impossible to be fast without doing something like the main action (here, running). A circumstance, on the other hand, is an independent situation existing beside the main situation (; cf. Lehmann & Shin 2005, ch. 3.3.5).

.Linda ran fast.
.Linda ran away despite Irvin's efforts to stop her.

Things are already more complicated in .

.We live like our forefathers.

Is this a manner construction or a comparison of equality?

The above criterion definitely does not apply to subordinate clauses. – contain manner clauses; – presents a circumstance clause.

.We live as our forefathers used to live.
.Erna öffnete die Tür, indem sie sich gegen sie warf.
Linda opened the door by throwing herself against it.
.Instead of pressing down the door handle, Linda threw herself against the door.
.Erna packte ihre Sachen, ohne dass jemand davon Notiz nahm.
Linda packed her belongings without anybody even noticing it.

is classified as a circumstance construction by the semantic criterion that it does not specify the manner of the superordinate proposition.

Just as with other interpropositional relations, the modal conjunctions of a language may be sensitive to the difference between identity vs. disjunctness of subjects. German wobei introduces either a manner or a circumstance, but indem ‘in’ is only possible with manners, as in .

A manner proposition ↴S may be unreal or hypothetical, as in and .

.Linda threw herself against the door as if she had never seen a door handle.
.Irvin drove as if the devil was after him.

The meaning of this construction may be paraphrased thus: ‘S↴S takes place in the way that it would take place if ↴S.’ In other words, there is a conditional ‘if ↴S, S↴S’ involved.

There is conceptual overlap between a manner clause and a comparative clause of equality. Thus, and might alternatively be considered as hypothetical comparisons of equality. Likewise, a circumstance clause resembles a temporal clause of simultaneity (s. Lehmann & Shin 2005 for some discussion).