Because that would be an extremely broad definition of art that I can't agree with. Sermons and pamphlets have a practical purpose. They may be well written, but so can an internal memo from a corporation, and nobody considers those to be art.
But just because something has a practical function, that doesn't mean it can't be art. We've had this in another thread already. This definition would rule out all architecture as art, for example. But surely any definition of "art" which precludes (say) a cathedral is a poor definition.
Moreover, what of art works such as the Sistine Chapel ceiling? Religious art such as that is intended to convey ideas to the viewer. It is not just art for art's sake. If having a practical purpose means something can't be art, then pretty much all religious art isn't art.
And we can say the same thing about the written or spoken word too. Isn't this art?:
William Shakespeare said:
Friends, Romans, countrymen, lend me your ears;
I come to bury Caesar, not to praise him;
The evil that men do lives after them,
The good is oft interred with their bones,
So let it be with Caesar ... The noble Brutus
Hath told you Caesar was ambitious:
If it were so, it was a grievous fault,
And grievously hath Caesar answered it ...
Here, under leave of Brutus and the rest,
(For Brutus is an honourable man;
So are they all; all honourable men)
Come I to speak in Caesar's funeral ...
He was my friend, faithful and just to me:
But Brutus says he was ambitious;
And Brutus is an honourable man
.
He hath brought many captives home to Rome,
Whose ransoms did the general coffers fill:
Did this in Caesar seem ambitious?
When that the poor have cried, Caesar hath wept:
Ambition should be made of sterner stuff:
Yet Brutus says he was ambitious;
And Brutus is an honourable man.
And yet that's serving all kinds of purposes. As a quote from
Julius Caesar, it is intended to entertain the audience, perhaps surprise or shock them. As a speech delivered by Mark Antony, it is intended to convey information to the crowd and, more importantly, turn them against Brutus and his co-conspirators in a subtle way without actually denouncing them. It is
rhetoric, and rhetoric is the artful use of language to convey ideas and emotions to the listener in a not always rational way.
But if a speech like that can be art, then why preclude sermons? Aren't they just exactly the same thing, but with a religious rather than a political purpose? Or at least they can be. Many preachers have used rhetoric just as artfully as any secular rhetorician. John Chrysostom was given that title - meaning "golden mouthed" - because of his ability to speak so beautifully; the title was occasionally given to great speakers, such as Dio Chrysostom. I defy anyone to read his sermons, or those of Gregory of Nazianzus, or of Basil of Caesarea, or of Augustine of Hippo, and say that these are not art simply because they are intended to convey ideas or convince the listener. On the contrary, they seek to do this
through the skillful use of art.
As for philosophy treaties, they're supposed to be scientific, and thus not art. I understand that's subjective and debatable, but I wouldn't call a treaty on philosophy an art form for the same reason I would not call a historical article or a book on physics.
Well, again, it's incumbent upon you to say why something that is "scientific" must, by definition, not be "art". What about the writings of Jacques Derrida, which seek to convey philosophical ideas through literary form? (I'll pass over the question whether Derrida really counts as a philosopher or not, since that's to do with the nature and worth of his ideas, not with the form in which he chooses to convey them.) Or take Plato's dialogues. Pretty much everyone agrees that these count as literature quite apart from their philosophical content, because of the charm and art with which they are written. Indeed, in antiquity they would probably have been read out loud by servants for the benefit of the master; there is thus a very fine line between these works of philosophy and full-blown performance art such as the work of the ancient Greek dramatists. Isn't it rather arbitrary to say that one text counts as art but another doesn't, just because it contains cognitive reasoning?
Well you were talking of educating and forcing ideas, which IMO is more coherent with sermons and pamphlets than art.
But any art form can convey ideas. It doesn't have to do so in a discursive fashion. Isn't
Paradise lost full of ideas and claims? Isn't it intended to make the reader think about these ideas? And isn't the Sistine Chapel ceiling also full of ideas which are intended to make the viewer think?