Linguistics
Linguistics studies language as a structured system, a cognitive process, a social practice, a learned capacity, and a changing historical object. These are different scales of the same communication loop.
Language is not only a dictionary plus grammar rules.
A speaker turns intentions into structured signals; a listener infers structure and meaning from those signals; both draw on learned conventions that vary across groups and change across time. Linguistics studies every part of that loop.
Language lives in a loop between structure, minds, communities, and time.
A linguistic system is not only grammar inside one speaker. People learn it, process it, vary it in social interaction, and change it across repeated generations of use.
The same language system can be studied over milliseconds, years, or centuries.
Different subfields often differ less in topic than in the timescale and population over which they ask the question.
Processing
How quickly can a listener recognize sounds, predict words, resolve ambiguity, and assemble sentence structure?
Learning & variation
How do individuals acquire patterns, adapt to interlocutors, and participate in socially structured variation?
Language change
How do repeated small variations accumulate into new sounds, words, grammatical systems, and language families?