Before we proceed, it is important to explain why these remarks are relevant. There are a few good reasons for revising some common patterns of English.
The first is that it allows us to perceive that the choice between two forms (both acceptable and described as more or less "equivalent" in several grammar books) is determined not only by the principles of end focus and end weight but also by the flow of discourse in connected sequences.
The following example shows an application of the principle of end-weight — a shift of the "heavier" components towards the end of the sentence:
(1) That Tom was prepared to go to such lengths astounded me
becoming
(1a) I was astounded that Tom was prepared to go to such lengths
The latter is perceived as much more natural in colloquial English, which means that frequency and unmarkedness do not always coincide. (1) must be chosen in sentences like
(1b) That Tom was prepared to go to such lengths astounded me, but not my brother who knew him well.
Here me bears primary stress and a rising, non-final intonation contour. The new information is that I was astonished because I did not know Tom.
Other pairs of syntactically "equivalent" sentences show similar patterns:
(2a) He gave all his heirlooms away.
(2b) He gave away all his heirlooms
(3a) The boy told mother all his secrets
(3b) The boy told all his secrets to mother
The theme-rheme order obviously changes and accordingly the choice depends on how the sequence continues:
(3a') The boy told mother all his secrets, which were beginning to worry him
(3b') The boy told all his secrets to mother, whom he trusted
The second reason is that an analysis of sentences in terms of kernel patterns, with their modifications and combinations, gives precise information on the syntactic complexity of texts. The control of complexity is essential in texts about science and technology (English for Specific Purposes or ESP) where simplicity can be of paramount importance. Only kernel patterns are used in certain types of oral communication.
A sentence like
(4) What we saw was horrible
as a whole is an example of Pattern 3 (S V C): X + be + adj. In its turn, the subject X derives from a Pattern 2 (S V O)
(4a) We saw Y
Let us now see a compound sentence:
(5) Words are fairly imprecise, yet their meanings can be tightened up
The first part is S V C, the second part is S V O passive, from
(5a) X can tighten up their meanings
Agent-less passive forms are very common in ESP as a device for de-personalisation. The following is a complex sentence:
(6) While the vocabularies differ, research has tried to show that there exist eleven basic colour categories
The main clause is S V O:
(6a) Research has tried to show + object (where the object is a clause)
The first subordinate clause is S V:
(6b) The vocabularies differ
The second subordinate clause is also basically S V:
(6c) Eleven [...] categories exist
but the there-extraposition has been applied.
As a general rule, the more complex a sentence is, the harder it is to read and understand it; this fact is well-known to journalists and copywriters (i.e. those who write texts for advertisements).