So I hear that all great apes can apparently use language and that they understand and use sign language just as humans do [more like children, but they can do it]. So my question is this: We know great apes, being one of them, have big brains. So maybe they are smart enough to know that if the make a few signs, they will get a reward. Even if they could associate the signs with objects and recombine them to form new words, but how do we know this association is not like pavlov's dog where the association is behavioural and not mental? Do they truely use language like us, using it for thinking, self reflection, making conscious decisions, feeling, understanding and expressing emotions and so on? If yes, how does it affect our perspective of them as animals? Should we consider them evolutionarily disadvantaged cousins [in a sympathetic way]? If they truely can use language like us, the lines between us and the rest of apes gets very much smudged indeed, doesn't it?