For a sociologist terms like "middle class" are not unproblematic, on the contrary. This is also true of terms such as "upper" and "lower class" as well as all other logically possible classes of this sort, for example, "uppermost", "lower upper", "higher middle", "lower middle", "upper lower", "lowest". Logically - and this is one of its problems - the ranking yardstick approach can produce an infinity of gradations. Why not, for example, refine it to accommodate "higher higher middle", "lower higher middle", "higher lower middle" and "lower lower middle"?

Translating this into percentiles does not dissolve the problem. This would not matter greatly if it were not that the whole point of this approach is to identify behaviourally homogenous social groups ranked according to some explicit criterion. The possibility of infinite subdivision makes this an elusive goal. Like Zeno's paradoxical arrow, the ranking approach to social class runs the risk of never reaching its goal.

Moreover, the question arises: Middle of what? According to which criterion is one higher or lower than another? Shall it be status, income, occupation, education, power or cultural taste? The variety of possible criteria presents us with the possibility of having individuals who are, say, high ranking in terms of power, middle ranking in terms of income and education and low ranking in terms of cultural taste.

Further, whereas some criteria lend themselves easily to ranking - such as the easily quantifiable criterion of "income" - some others - such as "status" and "power" - obviously do not. Take "power". If we exclude the easily quantifiable "purchasing power", how do we measure "political power" or the even more conceptually slippery criterion of power as the ability to activate informal networks to bend rules, jump queues and benefit from insider knowledge?

Even more problematic is the criterion of "status". Is it status in the eyes of the beholder or in the eyes of the beholden? In other words, is "middle class" something one "is" or something one wishes to be? Indeed, it can be argued that ranking by status is meaningless separately from the socially constructed meanings and values of historically concrete societies.

But what's new? Even our sociology undergraduates - assuming a decent course of studies, and the course has improved considerably under the present head of department - will have been confronted with these problems and with the fundamental debates they have generated throughout the history of this discipline. And, anyway, why should we bother with what could easily degenerate into a pedantic scholastic exercise?

Normally, therefore, one would not have picked on this subject for one's opinion column. But we do not live in politically normal times. As seen from my former philosophy professor's perspective, we are living a situation characterised by two political factors, two sides of a coin as it were. Firstly, we are witnessing the "dimming of (Lawrence Gonzi's) charismatic image", in Fr Peter Serracino Inglott's words "a symptom of non-adoption of the 1989 flash of hope" and "a reluctance to re-grow things from fresh roots".

Secondly, we have "Joseph Muscat... striving to present himself as the leader...of a movement that embodies the local equivalent of... the flash of hope that glimmered in the hearts and minds of all moderates and progressives throughout the world in that meteoric year 1989" (The Sunday Times, March 21)

I will come back to "the 1989 flash of hope", as Prof. Serracino Inglott calls it, a subject that I have referred to in this column three times in 2009 and once this year in connection with Fukuyama's now discredited thesis of the end of history.

What concerns me here is that, central to Dr Muscat's project of a movement of all moderates and progressives, is his recurrent reference to the middle class. To appreciate the political thrust of his use of this notion of "middle class", we must go beyond the narrow limits of traditional sociological discussion of social stratification.

To start with, it is important to note that Dr Muscat's insistence on the importance of the middle class in this country's future is not an opportunistic dernier cri. It is the result of sustained reflection within the Labour Party that goes back at least a quarter of a century.

It is pertinent to observe that a paper on the subject published in the Labour journal Society in, yes, 1989, has become a standard reference in academic discussion of class in Malta. Witness Ronald Sultana's Perspectives On Class In Malta of 1994 and JosAnn Cutajar's Social Inequality of 2009 in, respectively, Maltese Society: A Sociological Inquiry (R.G. Sultana and G. Baldacchino eds.) and Social Transitions In Maltese Society (J. Cutajar and G. Cassar).

As we shall see when we next meet again on this page, the political effectiveness of Dr Muscat's "middle class" will depend on its ability to rally all those who identify with the sort of society that he claims - sincerely, I believe - to promote. Although I have suggested that traditional sociological stratification debate will not help us much to understand his project, I am not saying that sociology is useless in this case. In fact, we would do well to look at "middle class" as an "interpellation" whereby those that respond to it need not share social origins or conditions but a vision of a shared future.

Dr Vella blogs at watersbroken.wordpress.com.