The observation which is to further understanding, which is to be acceptable to science, must itself be scientific. That is to say, it must be at once guided by foreknowledge, specially directed to what is essential in a phenomenon and its surroundings or conditions, and perfectly exact. If anybody supposes this to be easy, he should first try his hand at the work, and then compare what he has seen with what Darwin or Preyer has been able to discover. How difficult this is may be seen even with reference to the outward physical part of the phenomena to be observed. Ask any mother untrained in observation to note the first appearance of that complex facial movement which we call a smile, and you know what kind of result you are likely to get. The phenomena of a child’s mental life, even on its physical and visible side, are of so subtle and fugitive a character that only a fine and quick observation is able to cope with them. But observation of children is never merely seeing. Even the smile has to be interpreted as a smile by a process of imaginative inference. Many careless onlookers would say that a baby smiles in the first days from very happiness, when another and simpler explanation of the movement is forthcoming. Similarly, it wants much fine judgment to say whether an infant is merely stumbling accidentally on an articulate sound, or is imitating your sound. A glance at some of the best memoirs will show how enormously difficult it is to be sure of a right interpretation of these early and comparatively simple manifestations of mind.[4] ----- Footnote 4: These difficulties seem to me to be curiously overlooked in Prof. Mark Baldwin’s recent utterance on child psychology. (_Mental Development in the Child and the Race_, chap. ii.) In this optimistic presentment of the subject there is not the slightest reference to the difficult work of interpretation. Child-study is talked of as a perfectly simple mode of observation, requiring at most to be supplemented by a little experiment, and, it may be added, backed by a firm theory. -----