I don't think concepts are general ideas, by that I mean I don't think the formation of concepts is a matter of generalisation. A keyboard can be the board of keys of letters, numbers and symbols that you use to input data into a computer. It can also be a musical intrument. But we wouldn't call the control panel in a aeroplane's cockpit a "keyboard". How do we know how the generalisation works? We don't. It is partly down to human convention to see how to apply a concept. Concepts cannot be seperated from human understanding and human convention. We do not know all the applications of a concept when we apply it. Suppose a keyboard-like device is invented, how do we know whether it is a keyboard? When we decide, when the convention becomes fixed. Concepts are not seperable from their application. You could say a concept is a very particular thing with as much sense as saying that a concept is a general thing. It's nonsense to say we apply concepts to sense data.