Morphological change is the process by which a word's form changes over time. This can include changes to the word's root, affixes, or internal structure.

Semantic change is the process by which a word's meaning changes over time. This can include changes to the word's denotation, connotation, or usage.

Syntactic change is the process by which a word's syntactic function changes over time. This can include changes to the word's part of speech, its grammatical features, or its position in a sentence.

Phonological change is the process by which a word's pronunciation changes over time. This can include changes to the word's sounds, its stress pattern, or its intonation.

Morphological change can be caused by a variety of factors, including sound changes, analogical leveling, and back-formation.

Syntactic change can be caused by a variety of factors, including changes in the language's phonology, morphology, and semantics.

Semantic change can be caused by a variety of factors, including changes in the language's culture, environment, and technology.

Phonological change can be caused by a variety of factors, including changes in the language's speakers, environment, and technology.

Morphological change can have a variety of consequences, including changes in the language's syntax, semantics, and phonology.

Syntactic change can have a variety of consequences, including changes in the language's morphology, semantics, and phonology.

Semantic change can have a variety of consequences, including changes in the language's morphology, syntax, and phonology.

Phonological change can have a variety of consequences, including changes in the language's morphology, syntax, and semantics.

Studying morphological and syntactic change over time is challenging because of a variety of factors, including the lack of written records from earlier periods of a language's history, the difficulty of identifying and interpreting changes in a language's morphology and syntax, and the fact that morphological and syntactic change is often gradual and difficult to observe.

Linguists use a variety of methods to study morphological and syntactic change over time, including comparative linguistics, historical linguistics, and diachronic linguistics.

Research on morphological and syntactic change over time has a variety of applications, including understanding the history of a language, reconstructing proto-languages, and developing new methods for language teaching and learning.