Abstract: The present investigation is an attempt to study the relation between the understanding of causality and the mastery of causality conjunctions and the development of language in pre-school children. The experimental results obtained indicates:1) The understanding of causality and the mastery of causality conjunctions varies with age. Generally 5—6 years old children could master causality conjunctiods and it is difficult for 3—4 years to do so.2) The trend of the understanding of causality by pre-school children is: (a) from the reflection of external causes to the discrimination of latent internal ones; (b) from a global reflection of causal relation to a more differentiated and exact understanding; (c) from references to the concrete cause of the particular phenomenon to the reflection of a more general law.3) The mastery of the causality conjunctions (because... therefore) depends upon the understanding of cause-and-effect relation. It is essential, therfore, for children to understand such relations for the development of language in pre-school children.

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