In Beverly Hills they just demolished the 1961 Friar’s Club. In Chicago the big preservation issue is Bertrand Goldberg’s 1975 Prentice Women’s Hospital. Yet for many people, the idea of preserving buildings of the Recent Past is anathema. Often the dividing line is a generational one: our historic preservation students in their 20s and 30s have been excited about 1960s and 1970s architecture for a long time. Many people in their 50s and 60s are not.

There is an old saw that you don’t want to preserve something you saw built, but that is certainly not true for me. I got a camera when I was eight and took pictures of the not-yet-complete John Hancock tower in Chicago, and just over 20 years later there I was in front of it helping with a press conference to save a 21-year old building, already an icon of its city.

We had similar consternation when we discussed the Modernism and Recent Past efforts at the National Trust. Most accept the great architectural moments of Modernism, such as the Trust sites Philip Johnson’s Glass House and the Farnsworth House by Ludwig Mies van der Rohe. Even the legendary John Lautner’s architecture in Los Angeles is more widely understood, and you would find few in Chicago who did not think Goldberg’s 1965 Marina City was a landmark.

But the effort to save the Huntington Hartford Building on Columbus Circle in Manhattan was rife with contradiction: many hated the building since it arrived in 1962 and still hated it when they proposed to reclad the façade (which they did).

I bet you know what I am going to say next: it was always like this. The sliding window that is the Recent Past has always been a preservation problem. No in the field even liked Victorian architecture in the 1950s and 1960s. The first surveys of places like Charleston and Brooklyn pretty much stopped in the 1860s. There were Georgian societies in England and America but no Victorian societies and even in 1961 the experts thought it quite nutty that Greenwich Village residents wanted to save a building as ugly as Calvert Vaux’s Victorian Gothic Jefferson Market Courthouse.

Modernity itself can include a vast swath of history. Steve Kelley once brought Wessel de Jonge, one of the founders of DOCOMOMO, the first international organization for the preservation of Modernism, to my house, an 1872 Italianate. In the basement de Jonge looked up at the floor joists and asked with great enthusiasm whether he was looking at a balloon frame (which he was), because for him Brasilia began with some two-by-fours and nails in 1830s Chicago.

When people decry such Brutalist landmarks as the Boston City Hall, they are recalling widespread reaction against the buildings when they were built, often combined with rue at what they displaced. The 1960s are especially tricky because American culture went through its fastest evolution ever during that decade and the pace of change in the landscape was literally shocking. About faces were common: In Chicago’s Old Town people were in support of urban renewal efforts from 1956 to 1966 and then quite suddenly in 1967 they turned against renewal and started trying to save the existing fabric of the neighborhood.

This lovely 1961 bank in Chicago was denied landmark status because it was the Modernist outlier in a thematic designation of neighborhood banks. The prejudice against is often stronger than the sentiment in favor.

Brutalism, which emerged in the 1950s, has the double challenge of a bad label (it comes from the French for raw concrete, beton brut) and an aesthetic insistence that can be perceived as a kind of formal bullying.

But Victorian had an even worse rep for even longer, its demonization beginning in the 1910s as crisper Progressive Era styles supplanted it and reaching an apogee in the 1930s when cartoonist Charles Addams successfully married Victorian Second Empire style to ghoulish antisocial and murderous behavior. And Halloween. With the exception of a brief flicker of acceptance courtesy Disney’s 1954 Lady and the Tramp, Victorian remained anathema until the 1970s and the arrival of the Painted Lady in San Francisco.

Heck, the Prairie Style went out of fashion after less than two decades, and its practitioners were forced into uncomfortable Georgian and Tudor outfits through the 1920s. We can watch the current attempt to repair the PostModern Thompson Center in Chicago, barely 25 years old, and recall that it was so reviled its architect did not erect a major building in his home city for almost 20 years.

But the most revelatory thing that has happened in my life is that I have witnessed buildings – their architecture and design – change without changing at all. There are buildings I saw built or knew shortly after they were built in Oak Park and when I looked at them in the 1970s and 1980s I knew they were ugly. But then in the late 1990s they were no longer ugly. By the early 2000s they were becoming beautiful, and of course nothing had changed about them.

Our appreciation of the past is a sliding window. Like the act of conserving our built environment, it is not a standard or a rule or a fixed canon, but a process, wherein a culture and generations of people examine themselves and determine what elements of the past are important at that moment in time.