This might sound like a crazy bad question. But I'm wondering even though current and voltage inevitability co-exist, why do we use the term for one concept(current or voltage)? If there is a signal out there somewhere, it is both current and voltage at the same time. But we name only one of its property.
Is that about knowing one of them well? I mean lets say we have an amplifier and if we only set the amplifier with a "known voltage gain" we call it voltage amplifier and if we set it with a "known current gain" we call it current amplifier? Or is that because the nature of the input signal?
Could you give an input signal example and explain why it is called a voltage or current signal?
EDIT: My confusion didn't settle. Lets say we have a single stage amplifier. And it has an input and output. So when you look at such circuit and its input and output, what makes you to conclude it is amplifying a current input signal or a voltage input signal? What is the method to name the type of the input signal? Imagine it is increasing both. I still don't understand how to distinguish.
EDIT2: imagine a typical common emitter stable biased single npn bjt transistor amplifier. such as: http://www.electronics-tutorials.ws/amplifier/amplifier9.gif?81223b . the base voltage in this case is "bias voltage + small signal voltage - emitter voltage". and the input current current is very low. now look at the output. output voltage increased. okay. but wait.. output current also increased and became "beta*Ibase". So now the input current increased and the input voltage also increased.. is this a current or voltage amplifier? and if it is X amplifier does that mean the input signal is X signal. (X is current or voltage)