It is very evident that there is no one situation which will necessarily
take either free or forced attention because the determining factor is
not in the situation _per se_, but in the relation it bears to the mind
engaged with it. Sometimes the same object will call forth forced
attention from one person and free from another. Further, the same
object may at one time demand free attention and at another time forced
attention from the same person, depending on the operation of other
factors. It is also true that attention which was at first forced may
change into free as the activity is persevered in.

Although these two types of attention are discussed as if they were
entirely separated from each other, as if one occurred in this situation
and the other in that, still as a matter of fact the actual conditions
involve an interplay between the two. It is seldom true that free
attention is given for any great length of time without flashes of
forced attention being scattered through it. Often the forced attention
may be needed for certain parts of the work, although as a whole it may
take free attention. The same thing is true of occasions when forced
attention is used. There are periods in the activity when free attention
will carry the worker on. Every activity, then, is likely to be complex
so far as the kind of attention used, but it is also characterized by
the predominance of one or the other type.

The question as to the conditions which call out each type of attention
is an important one. As has already been said, free attention is given
when the situation attended to satisfies a need. Physiologically stated,
free attention is given when a neurone series which is ready to act is
called into activity. The situations which do this, other things being
equal, will be those which appeal to some instinctive tendency or