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Subject manipulation in texts
Explanation of active and passive sentences
Active sentences are transitive sentences (having predicators that take
objects) which have the actor of the sentence as its subject, as in:
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S
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P
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O
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A
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Mary
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¦ placed ¦
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the copper sulphate
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¦ in the test-tube
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Here, 'Mary' is the subject of the sentence, the topic of the sentence
(who it is about) and also the actor or agent (the person who carries
out the action).
But now let's reorganise the sentence so that the copper sulphate is
the topic of the sentence. We would then get:
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S
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P
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A
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A
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The copper sulphate
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¦ was placed ¦
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in the test-tube
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¦ by Mary
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Now the thing which is acted upon (the Goal of the action), 'the copper
sulphate', is the subject (reflecting its topic-hood); and the agent,
Mary, has been moved from the subject position and turns up in a prepositional
phrase (PP: 'by + NP = agent') acting as an adverbial. In other words,
the two typical functions of the subject (topic and actor/agent) have
been split apart.
Now that the sentence has been made into a passive, it is also possible
to delete the 'by + agent' phrase:
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S
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P
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A
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The copper sulphate
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¦ was placed ¦
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in the test-tube
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Notice that this has now become the language of the scientific experiment.
The agent has been removed, giving this sort of structure, in context,
an 'objective, scientific' feel which is appropriate for science. For
the experiment, it doesn't matter who places the copper in the test-tube,
as long as it gets there! This is why scientific language is often associated
with the passive construction. Active sentences demand an agent/actor
as subject (and so also as topic). Passives do not, however, and once
a sentence is passivised the resulting 'by + agent' phrase can be deleted
because, in SPOCA terms, it is an Adverbial, the most optional of the
SPOCA elements in English sentences.
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