In structural terms, the passage is curiously homogeneous; all seven sentences belong to the same grammatical, textual and discoursal categories: declarative, statement, informative. We need a more informative analysis but that can only be achieved by relating each sentence to both its co-text – the sentences around it – and its context; the speech acts surrounding it.

We can begin by noticing markers of cohesive relations which will allow us to decide whether a sentence could be the first in the text.

1. The user of English instantly recognizes it, despite the shared content, as something else: an apology.

In terms of bottom-up processing, we can parse the linear sequence and recognize that 'it' must refer back to some earlier nominal in the text (an example of the substitution of a proform – a pronoun – to make anaphoric reference) and infer from that that (1) is not the first sentence of the text. Equally, from the top-down point of view, even though we cannot be sure what the discourse function of the sentence is (other than crudely 'informative') until we have reorganized the text, we will already have recognized, even from this first sentence with its unqualified assertion, relatively complex syntax and abstract technical terminology having the structure 

definition + example(s) + comment(s) 

that this is a didactic and metalinguistic text, probably from a textbook or a paper in linguistics or a linguistically oriented sub-domain of one of the human sciences.

2. This, as a speech act, is one of simple reference: the content is the burning of the toast and my attitude to that event is merely that of a reporter.

'This' also refers back; a deictic with anaphoric reference. (2) cannot, therefore, be the first sentence either and, like (1), its speech act/ functional status cannot be specified beyond the very general 'informative'. The sentence, however, provides further evidence in support of our initial assumption that the domain of this text is metalinguistic. Even in purely lexical terms the conclusion seems irresistible; 'speech act’, 'reference' and (a second time) 'content'. Acting on this hunch (until there is good reason to change our minds), we recall what we know about didactic written discourse in general and about linguistics in particular and could, at this point, rush ahead and look for a definition, since we expect such texts to begin with definitions. However, we shall be cautious and continue our sentence-by-sentence reading and analysis.

3. For example, I can refer, in a completely neutral way, to a past action of my own and say 'I burned the toast this morning'.

'For example' is also anaphoric; a reference to some earlier element of the text which is to be reintroduced and exemplified. (3) cannot be the first sentence either and is marked by the phrase 'for example' as functioning as an example.

4. In simple terms, a speech act consists of its content + the orientation of the speaker to that content and these together give the speech act its social meaning.