Freud

So long as we trace the development from the final stage backwards, the connection appears continuous, and we feel we have gained an insight which is completely satisfactory or even exhaustive. But if we proceed the reverse way, if we start from the premises inferred from the analysis and try to follow these up to the final results, then we no longer get the impression of an inevitable sequence of events which could not be otherwise determined. We notice at once that there might have been another result, and that we might have been just as well able to understand and explain the latter. The synthesis is thus not so satisfactory as the analysis; in other words from knowledge of the premises we could not have foretold the nature of the result. it is very easy to account for this disturbing state of affairs. Even supposing that we thoroughly know the etiological factors that decide a given result, still we know them only qualitatively, and not in their relative strength. Some of them are so weak as to become suppressed by others, and therefore do not affect the final result. But we never know beforehand which of the determining factors will prove the weaker or the stronger. We only say at the end that those which succeeded must have been the stronger. Hence it is always possible by analysis to recognize the causation with certainty, whereas a prediction of it by synthesis is impossible.