Expect a large orchestra. At the end of next week, the Seattle Symphony will simultaneously close its regular concert season and open its...

Expect a large orchestra. At the end of next week, the Seattle Symphony will simultaneously close its regular concert season and open its Summerfest with a double sonic spectacle of Wagner and Mahler.

The concerts, which begin on Thursday and run through the following Sunday afternoon, specifically feature the beginning and ending movements of Wagner’s opera “Tristan und Isolde,” featuring international operatic superstar Jane Eaglen, and Mahler’s Sixth Symphony, with its dramatic hammer blows of fate.

So what do these two works have in common, besides Teutonic immensity? A lot, as it turns out. An hour before each concert, professor Eric Hanson of Seattle Pacific University, author of “Mahler and the Will,” ties threads together between the two 19th-century composers and the artistic climate of their time. The preconcert lecture is called “The Tristan Chord and Its Resonance: Wagner, Schopenhauer and Mahler.”

A central connection between these two composers is the philosophy of Arthur Schopenhauer, who argued that the will of man was a more powerful force than even the intellect, and that our suffering from this could only be salved by art. And foremost among the arts, according to the philosopher, was music.

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Naturally, this is a philosophy that composers are easily attracted to. But Wagner and Mahler both went further than that. Wagner based the plots of three of his operas (including “Tristan”) on Schopenhauer’s philosophy of the human will, and Mahler even created a musical figure called the “life-will motive” that he used in every symphony — except one.

“It’s a bit of ironic programming,” Hanson pointed out in a recent conversation. “The Sixth Symphony is the only one of Mahler’s that does not have this melodic figure.” Its very absence, however, speaks volumes. Known as the “Tragic” Symphony, the absence of a life-will motive may have reflected Mahler’s prescient fears at the time, since in the following years tragedy would strike his family and he would learn of his own dangerous heart disease.

But Hanson will also focus on a musical theme that is very present in the Wagner we will hear: the Tristan chord. So how important could a chord be? This one shook up the artistic world in ways that few other musical moments have. Though the notes F, B, D sharp and G sharp had been used in combination before, Wagner was the first to shine an extended spotlight on them in a way that stretched the concept of tonality itself and led to the musical revolutions of the early 20th century.

It occurred at a time when political and scientific thought were also experiencing revolutionary breakthroughs, with Darwin, Marx and John Stuart Mill. It shattered musical boundaries and upset the musical establishment. It opened up all sorts of new possibilities for every composer who came after him, including Mahler.

Whether you want to close out the concert season, open up the new one or get a foretaste of the 2009 Wagner festival, we all have some music to look forward to that is both titanic and intricate.