There is a debate I'm having with someone over whether something can just be aesthetic.
Such as:
"The dog is aesthetic." "The world is aesthetic." "That tree is aesthetic."
It's starting to sound a little more correct as I read it but it sounds so incorrect.
The word can be used as an adjective; for example, "The dog has aesthetic appeal". And it can also be a noun, as in, "The dog adheres to its breed's aesthetic". But as an adjective in "The dog is aesthetic", it is not idiomatically correct.
I'm not sure what the general rule at play is, but it's English so there may not even be a general rule!
Technically, you can say those things. "The dog is aesthetic." "The world is aestheitc." "That tree is aesthetic." There is nothing wrong with these sentences.
The correct usage of the word aesthitic lies in what you mean to say by it.
Like Colleen V said, the word aesthetic is not a synonym of the word "beautiful" which is the actual state of having or being considered to have beauty. Instead it means "relating to, or concerned with beauty, emotions, and the senses" (Source).
Keeping this in mind, there's only two ways that this word has been seen to be used in my experience, when being used as a descriptor for a noun:
Now, if we apply these two rules to the second example you mentioned,
The world is aesthetic.
You could mean:
The world is an aesthetic place.
Meaning the place itself or the things that the place consists of, are capable of inducing thoughts relating to beauty.
Or assuming that by 'the world' you mean 'all beings in the world', you could mean:
The beings of this world are aesthetic ones.
Meaning that they are capable of considering, or like to consider ideas related to beauty.
Now, depending on what your opinions are, and what you are trying to convey by using the word aesthetic, the other two sentences can also be correct. Nevertheless, it is important to be clear about what one is trying to say, so if these sentences were to be truly "correct", they would use other words to explain how the word aesthetic applies in those particular cases. Like the way demonstrated above when the second sentence was used as an example.
I've been seeing "aesthetic" tossed around in the weight lifting community as shorthand for bodybuilders that lift only to develop aesthetic qualities. They'll say something like, "That's so aesthetic, brah", and it's mindnumbing in how wrong it sounds. Even more so when you see it outside of that context among people that you might not expect like in art or film criticism (generally by common laypeople, not professional critics or writers). Irks me something fierce.
I have seen the word and used the word most often as an adverb,
People will enjoy looking at your dog; his fur is aesthetically pleasing.
And I think the answer to, can the dog itself be aesthetic, is yes but just less common, so it sounds off. In comparison to other adverbs that typically describe an adjective it's ok to do this.
The a long awaited cheesecake was wonderfully rewarding.
Originally wonderful was describing the adjective rewarding, but it's perfectly acceptable to just call the cake wonderful, which is a simpler sentence.
So then, if the dog can be aesthetically pleasing we can jump to the punch and just call the dog aesthetic. I don't see any way to suggest that's not correct and can't think of a more correct usage of the adjective form of this word.
Understanding who uses the term in this manner is also important. This particular idiomatic use has risen from what I'd only describe as jocks on the internet, possibly ironic in origin. Though that gives rather more credit than is due. Assuming this is the use you're asking about the answer is no. It cannot be used as a synonym for attractive, for reasons others have stated.
