Post-tenure, if you don’t do research, you would end up teaching two courses per semester.

That, of course, depends on one’s institution

Yes, certainly, sorry for misleading anyone.

 where I teach the load is a 4-4 (to those outside of the profession, that means 4 courses per semester).

So that easily sounds like 40 hours a week to me. Of course, the prep time will depend on the course and the field, but still...

And, I forgot to also mention student advising. I currently have 5 Ph.D. students. Let's say I meet with each student an hour a week, and spend an additional hour per week thinking about the problem they are working on. That's 10 hours already.

Or, how about proposals? The current acceptance rate at NSF is about 2%-10% in my discipline.

Then there are papers, of course. Let's say I publish five good papers a year. Each of these papers easily takes a week just to prepare, even with grad student assistance.

Post-tenure, if you don’t do research, you would end up teaching two courses per semester.

That, of course, depends on one's institution--where I teach the load is a 4-4 (to those outside of the profession, that means 4 courses per semester).

Post-tenure, it is true that one could slack off, but there are also slackers at companies. Also, there is a lot of dead weight in the staff at my state university, who essentially cannot be fired.

Post-tenure, if you don't do research, you would end up teaching two courses per semester. That is four lectures per week. Each lecture probably takes 5 hours to prepare for. That's 20 hours a week right there. Add in grading, office hours, making up assignments, writing recommendations, meetings, and just keeping up with your field, and you can easily hit 40 hours a week, even with a TA to help out.

I think there’s a great divide in the academic world between the tenured and the non-tenured. Practically all of the criticisms of the academic life are justified about the tenured. Practically none are about the non-tenured.

I think that this is true in terms of the perception of those doing the criticizing.

However, speaking as one who has lived as both a non-tenured (both an a non-tenure-track instructor and a tenure-track assistant professor) and a tenured associate professor, I can say with some authority that getting tenure does not equate to a decision to stop working hard. Indeed, i have been busier since getting tenure than I was before I earned it, serving three years as Faculty Council President and having written a book, amongst other things plus everything else I did pre-tenure.

Now, granted, I still have full professor to shoot for, but that is mostly a prestige thing, as it does not affect my tenured status nor does it equate to a substantial raise in pay (indeed, it amounts to a rather disappointing raise in pay :).

Even once I hit full professor, which I very much expect to happen, I don't forsee any special change in my work habits.

And I would note, that I observe similar behavior from my colleagues at my university, and from my colleagues in broader academia.

James hits on a key reason:

There’s a job to be done and professional pride motivates me to do it.

And really, to be a Ph.D. in the first place requires a great deal of self-motivation driven by something other than monetary renumeration, so by the time one has hit tenure, it isn't like one's personality changes and one gets lazy.

Look: the academic life is a good one, and that was part of my motivation for entering it. I certainly am not complaining, but it does get a bit tiresome when one is told that one isn't working very hard, as is frequently the case in public discourse about the professoriate.

On the one hand, most people don't like to be accused of not working hard (especially when one knows that one does, in fact, work hard), but on the other, it beats digging digs and has a schedule that is radically more flexible than those of the vast majority of the population.

Indeed, doing the things that get you tenure often distracts from doing the things you need to do to be a good teacher.