diff --git a/books/psicologia/psychology-of-intelligence.mdwn b/books/psicologia/psychology-of-intelligence.mdwn
index a725a4cab0e455360c907aefe509fc40d2fce730..0693de4e1a6ff23a1aa5d3c3c77c68971df82a3c 100644
--- a/books/psicologia/psychology-of-intelligence.mdwn
+++ b/books/psicologia/psychology-of-intelligence.mdwn
@@ -2,6 +2,10 @@
 
 * Author: Jean Piaget
 
+## Main topics
+
+* Intelligence is reversible.
+
 ## Logic and psychology
 
     An axiomatics is an exclusively hypothetico-deductive sci-
@@ -70,3 +74,73 @@
     but do not ensure their future conquests. 1
 
     -- page 34
+
+## Habit and sensori-motor intelligence
+
+Circular reaction:
+
+    Let us imagine an infant in a cradle with a raised cover from which
+    hang a whole series of rattles and a loose string. The child grasps
+    this and so shakes the whole arrangement without expecting to do
+    so or understanding any of the detailed spatial or causal rela-
+    tions. Surprised by the result, he reaches for the string and
+    carries out the whole sequence several times over. J. M. Baldwin
+    called this active reproduction of a result at first obtained by
+    chance a “circular reaction”. The circular reaction is thus a typ-
+    ical example of reproductive assimilation. The first movement
+    executed and followed by its result constitutes a complete action,
+    which creates a new need once the objects to which it relates
+    have returned to their initial stage; these are then assimilated to
+    the previous action (thereby promoted to the status of a schema)
+    which stimulates its reproduction, and so on. Now this mechan-
+    ism is identical with that which is already present at the source
+    of elementary habits except that, in their case, the circular reac-
+    tion affects the body itself (so we will give the name “primary
+    circular reaction” to that of the early level, such as the schema of
+    thumb-sucking), whereas thenceforward, thanks to prehension,
+    it is applied to external objects (we will call this behaviour affect-
+    ing objects the “secondary circular reaction,” although we must
+    remember that these are not yet by any means conceived as
+    substances by the child).
+
+    -- 110-112
+
+Early intelligence:
+
+    The routes between the subject and the object fol-
+    lowed by action, and also by sensori-motor reconstitutions and
+    anticipations, are no longer direct and simple pathways as at the
+    previous stages: rectilinear as in perception, or stereotyped and
+    uni-directional as in circular reactions. The routes begin to vary
+    and the utilisation of earlier schemata begins to extend further in
+    time. This is characteristic of the connection between means and
+    ends, which henceforth are differentiated, and this is why we
+    may begin to speak of true intelligence. But, apart from the
+    continuity that links it with earlier behaviour, we should note the
+    limitations of this early intelligence: there are no inventions or
+    discoveries of new means, but simply application of known
+    means to unforeseen circumstances.
+
+    -- 114
+
+Innovation:
+
+    Two acquisitions characterise the next stage, both relating to
+    the utilisation of past experience. The assimilatory schemata so
+    far described are of course continually accommodated to
+    external data. But this accommodation is, so to speak, suffered
+    rather than sought; the subject acts according to his needs and
+    this action either harmonizes with reality or encounters resist-
+    ances which it tries to overcome. Innovations which arise for-
+    tuitously are either neglected or else assimilated to previous
+    schemata and reproduced by circular reaction. However, a time
+    comes when the innovation has an interest of its own, and this
+    certainly implies a sufficient stock of schemata for comparisons
+    to be possible and for the new fact to be sufficiently like the
+    known one to be interesting and sufficiently different to avoid
+    satiation. Circular reaction, then, will consist of a reproduction
+    of the new phenomenon, but with variations and active
+    experimentation that are intended precisely to extract from it its
+    new possibilities.
+
+    -- 114