Corruption or bastardisation refer to the idea that language change constitutes a degradation in the quality of a language, especially when the change originates historically from human error or prescriptively discouraged usage. Descriptive linguistics typically does not support this concept, since from a scientific point of view such changes are neither good nor bad.
Words are commonly said to be "corrupted" or "bastardized" if they undergo a change in spelling or pronunciation when borrowed from one language to another (e.g. "Cajun" [from "Acadian"]). This example illustrates that normal phonological developments (in this case, palatalization of /dj/ to /dʒ/) can be labeled by some as "corruption", a position which demands that any language change from a previous state be thus labeled. In this view, English would be a "corruption" of Proto-Germanic, the Romance languages would be "corruptions" of Latin, and Latin would ultimately be a "corruption" of Proto-Indo-European.
Language corruption may refer to a change in words, as described above, or to a deviation from the so-called "purity" of standard language. For example, the split infinitive has long been disputed as either a corruption or norm of the English language, even though the concept of the English infinitive containing the preposition "to" is challenged by usage with modals (can, shall, must, etc.) which precludes employing to. A language (or a certain variety of it) can also come to be regarded as having become "corrupted" if it has acquired a large vocabulary from other languages. This terminology is highly frowned upon by most academic linguists, as the adoption of loan words is a normal process which has no effect on the functionality of the language. Labeling a language as "corrupted" is a subjective value judgement which often leads to linguistic discrimination.
Text bastardisation refers to an unrelated process, namely the alteration and publication of a text in a way inconsistent with the original purpose or the author's intention. In cases which involve the removal of allegedly "inappropriate" content from a work, this is also known as bowdlerization.