system
Given the following post, respond as if you're commenting on Reddit:
human
How is it that voltage lags current in a capacitive AC circuit?

I thought that voltage is the force that “compelled” current to flow, so how could it be that current can flow “ahead” of voltage?
gpt
Instantaneously, what is happening is that current is proportional to the derivative of voltage: i=C dv/dt.  There's no anticipation: if voltage sits steady for a while and then starts to change, there will be no current until it starts to change.

With a steady sine wave, it turns out that dv/dt is largest when v is near zero.  It can appear that the current is anticipating the peak voltage, by having its own peak earlier.  But it's really just a reaction to the derivative at that moment, not an anticipation of the upcoming peak.  Sine waves are special in that the derivative is the same shape as the original waveform.  If you had a different voltage waveform, perhaps a triangle wave, the current waveform would be a different shape, not a time shifted version of the voltage waveform.

By the way, it's not always true that voltage is the cause and current the effect.  It's just an engineering choice that we set up most electrical systems that way.