A Realist Theory of Science Roy Bhaskar

93 A Realist Theory of Science
instantiated and it has been independently verified. But both
antecedents and consequents are events in open systems. Is there not
an asymmetry here? Am I not placing a higher demand on
antecedents than consequents? Ontologically no; but epistemically
yes. For a mechanism may be set in motion and because of the
complexity or opacity of the conditions under which this happens the
describer may not know that it has been set in motion; so that a
fortiori he cannot know that the law it grounds is applicable. To
explain an event by invoking a law I must have grounds for supposing
that a mechanism is at work; but the mechanism may be at work,
given that its stimulus and other conditions are satisfied, without my
knowing it. Some fields may be incapable of detection.
In §2 the critical conditions for a closure were developed and in §3
the concept of action implied by them was brought out. In both cases
their restrictedness was noted. In this section a realist account of laws
has been counterposed to the actualist account and its superiority
clearly demonstrated. Once we are persuaded of the very special
conditions presupposed by actualism and the possibility of an
alternative, what havoc must we make of the doctrines of orthodox
philosophy of science?
In nature, constant conjunctions are the rare exception; not, as
supposed by actualism, the universal rule. And in general it requires
human activity to generate them. To invoke a law I must have
grounds for supposing that the antecedent conditions are satisfied, so
that the mechanism designated is active. But it is only if I have
grounds for supposing that the system in which the mechanism acts is
closed that the prediction of the consequent event is deductively
justified. With this in mind let us return to the theories expressed in
statements (i)–(v) on pages 63–4 above. It is only under conditions of
a closure that given the antecedent, the deduction of the consequent
event is possible, so that the conditions for the Popper-Hempel theory
of explanation are satisfied (ii) or those for the symmetry between
‘explanation’ and ‘prediction’ obtain (iii). It is only then that ex ante
criteria of refutation can be laid down for a theory (iv) or that it
makes sense to judge a theory by its predictive success (v). For it is
only then that the resemblances and sequences between phenomena,
that Mill identified and so confused with laws, are constant (i).
It is contingent whether some enduring thing or mechanism is
activated. And though, given this, it is necessary that a certain