Gorgias has argued (see here and here) that there isn't anything and (see here) that, even if there were anything, you wouldn't be able to think about it. Now he argues that, even if there were anything and you could think about it, you wouldn't be able to communicate it to anyone.
1. We communicate with language. Language about things that are is not the things that are. So we don't communicate the things that are. We communicate language. The only thing that gets transferred to another person isn't the thing we saw but our words about it. We can't make perceptual images into sounds and vice versa, so we also can't make external objects into language. So the things that are, even if they could exist and be thought of, could not be communicated.
2. Language comes to us just as flavors do. It's an external thing we perceive with senses (visually or aurally). We might be inclined to think of this as language revealing some external object, but that's backwards. We have the language, and we posit an external object to explain the language just as we posit an external object to explain the image we see or sound we hear. (We posit a Grand Canyon when we hear someone tell us they went there.)
3. Language isn't really an object the way visible and audible things are. Even if it is, it's not similar to visible objects. It's grasped by a different organ. So language doesn't reveal these objects that are dissimilar from it.
4. Objects can't reveal each other's nature. So language, which is even more different, can't reveal other objects.
1. Couldn't there be something in our mind when we hear them describe something that's similar to what's in someone else's mind when they see it?
2. We do posit an external object when we hear about it or read about it. We also posit an external object when we see it or touch it. How does that mean the object doesn't exist? How does it mean we can't communicate about it?
3. Language is distinct from the things it is about, but that doesn't mean it doesn't represent those things in a way that it can cause us to think about them. It doesn't mean we can't communicate something by using it.
4. Language doesn't connect us with the very essence of the things it's about, but it does communicate something that allows us to envision some features of those things.