constructed out of elements intended to provide clues to both the meaning and the pronunciation. However, as both the meanings and pronunciations of the characters have changed over time, these components are no longer reliable guides to either meaning or pronunciation. The failure to recognize the historical and etymological role of these components often leads to misclassification and false etymology. A study of the earliest sources (the oracle bones script and the Zhou-dynasty bronze script) is often necessary for an understanding of the true composition and etymology of any particular character. Reconstructing Middle and Old Chinese phonology from the clues present in characters is part of Chinese historical linguistics. In Chinese, it is called Yinyunxue (). Pictograms Roughly 600 Chinese characters are pictograms () – stylised drawings of the objects they represent. These are generally among the oldest characters. A few, indicated below with their earliest forms, date back to oracle bones from the twelfth century BCE. These pictograms became progressively more stylized and lost their pictographic flavour, especially as they made the transition from the oracle bone script to the seal script of the Eastern Zhou, but also to a lesser extent in the transition to the clerical script of the Han dynasty. The table below summarises the evolution of a few Chinese pictographic characters. Simple ideograms Ideograms () express an abstract idea through an iconic form, including iconic modification of pictographic characters. In the examples below, low numerals are represented by the appropriate number of strokes, directions by an iconic indication above and below a line, and the parts of a tree by marking the appropriate part of a pictogram of a tree. N.B.: - a tree () with the base indicated by an extra stroke. - the reverse of , a tree with the top highlighted by an extra stroke. Compound ideographs Compound ideographs (), also called associative compounds or logical aggregates, are compounds of two or more pictographic or ideographic characters to suggest the meaning of the word to be represented. In the postface to the Shuowen Jiezi, Xu Shen gave two examples: , formed from and , formed from (later reduced to ) and Other characters commonly explained as compound ideographs include: , composed of two trees , composed of three trees , depicting a man by a tree , depicting a hand on a bush (later written ) , depicting a hand above an