A proportional comparative construction is a construction of the following form: There are two propositions, subordinate ↴S and superordinate S↴, each containing a predication or modification based on a scalar parameter. Both propositions embody the notion that this predication or modification may reach a series of successive points on the respective parameter, directed towards one of its poles. The construction says that the progression on the parameter relevant in ↴S is proportional to the progression on the parameter relevant in S↴. This proportional correlation generally implies that the progression of S↴ depends on the progression of ↴S. and are examples.

.To the extent that people become aware of their conditions, they vote for leftist parties.
.As we were climbing to the top, breathing became increasingly arduous.

These are no grammatical constructions specifically dedicated to the function at hand. features a lexical circumlocution, while uses the generic subordinative conjunction of a comparison of equality (as) to convey the parallel development of the two propositions.

In languages which have polar adjectives, these are the choice means to code scalar parameters. is an example using these.

.Je schneller das Karussel sich drehte, desto schwindliger wurde mir.
GermanThe faster the carousel turned round, the dizzier I got.

illustrates a syntactic construction dedicated to proportional comparison. Here, both ↴S and S↴ are coded by clauses containing a scalar adjective or adverb. In , the parameter relevant in ↴S is speed, coded by an adverb, while the parameter relevant in S↴ is dizziness, coded by an adjective. The following structural properties are commonly observed in proportional comparative constructions:

  1. The adjectives or adverbs are somehow marked for the gradation. In SAE languages, this involves the comparative degree, however morphologically coded.
  2. The construction takes the form of a correlative diptych:
    1. The subordination is some kind of adjunction.
    2. The conjunctions are typically distributed in correlative fashion across the two clauses.
  3. The correspondence of the two parameters and the interdependence concerning their gradation is signalled by the clause-initial position of the constituents containing the adjectives or adverbs.

Concerning feature #2a, the construction may be inverted, as in ', but the subordinate clause can hardly be embedded. '' is, though possibly grammatical, improbable to occur.

'.Mir wurde desto schwindliger, je schneller das Karussel sich drehte.
''.Mir wurde, je schneller das Karussel sich drehte, desto schwindliger.

As for feature #2b, the correlative nature of the binary conjunctions is clear from their morphological form in the Portuguese version of , viz. .

.Quanto mais depressa o carrocel virava, (tanto) mais ourado ficava eu.