- Economy: Speech communities tend to change their utterances to be as efficient and effective (with as little effort) as possible, while still reaching communicative goals. Purposeful speaking therefore involves a trade-off of costs and benefits.
- Expressiveness: Common or overused language tends to lose its emotional or rhetorical intensity over time; therefore, new words and constructions are continuously employed to revive that intensity
- Analogy: Over time, speech communities unconsciously apply patterns of rules in certain words, sounds, etc. to unrelated other words, sounds, etc.
- Language contact: Words and constructions are borrowed from one language into another.
- Geographic separation: When people with one language move away from each other, the language will gradually diverge into separate dialects, due to different experiences.
- Cultural environment: As a culture evolves, new places, situations, and objects inevitably enter its language, whether or not the culture encounters different people.
- Migration/Movement: Speech communities, moving into a region with a new or more complex linguistic situation, will influence, and be influenced by, language change; they sometimes even end up with entirely new languages, such as pidgins and creoles.
- Imperfect learning: According to one view, children regularly learn the adult forms imperfectly, and the changed forms then turn into a new standard. Alternatively, imperfect learning occurs regularly in one part of society, such as an immigrant group, where the minority language forms a substratum, and the changed forms can ultimately influence majority usage.
- Social prestige: Language may not only change towards features that have more social prestige, but also away from ones with negative prestige, as in the case of the loss of rhoticity in the British Received Pronunciation accent. Such movements can go back and forth.
According to Guy Deutscher, the tricky question is "Why are changes not brought up short and stopped in their tracks? At first sight, there seem to be all the reasons in the world why society should never let the changes through." He sees the reason for tolerating change in the fact that we already are used to "synchronic variation", to the extent that we are hardly aware of it. For example, when we hear the word "wicked", we automatically interpret it as either "evil" or "wonderful", depending on whether it is uttered by an elderly lady or a teenager. Deutscher speculates that "[i]n a hundred years' time, when the original meaning of 'wicked' has all but been forgotten, people may wonder how it was ever possible for a word meaning 'evil' to change its sense to 'wonderful' so quickly."