The stage where summarization properly occurs in the automatic production of condensation. However, the focus of past and current work on automatic summarization has been on the selection/extraction of important sentences, and the question of what is involved in condensation has very much been unexplored. While there is some recent work in the production of concise sentences, some of the "operations"/"transformations", e.g. moving the subject from the end to the front, may not be considered as condensation processes. Via a comparative study of sentences in document and abstract, our study which does not aim to produce any concise text, but to better understand the process of condensation itself, identified some of the major linguistic operations in abstracting by an individual author himself, to be substitution, deletion, aggregation, compression, and modification. While the processes rarely operate alone, we will only discuss on one process, namely substitution. On the basis of form and substitutability, the study which was carried out on entomology-related journal articles with author written abstracts, identified four types of substitutes which we will illustrate and discuss with examples extracted from our corpus.