I would suppose that the value of the actual item is immaterial to its gravity. However, the value of the item to the individual that it was stolen from is intrinsic to its grave nature.
The Catholic Encyclopedia has a good breakdown on the definition of ‘theft’: *The grievousness of theft seems to depend on the way in which the purposes which make the respecting of property rights obligatory are set at naught. These ends are, first the preservation of peace and harmony among individuals, and then the guaranteeing of the security of human society, as well as the providing an incentive for each one to pursue an industrious career. A man who steals may bid defiance to either or both of these ends. So far as the first is concerned it is obvious that the unjust appropriation of goods to such a value as to destroy this concord and furnish reasonable ground for great sorrow to the owner must be reputed a mortal sin. That amount is clearly not a constant quantity. It will vary according to the circumstances of the person injured as well as of place and time in which commodities may be more or less valuable. It will even take account of the special relationship which perchance the thief holds to the one he has despoiled, as when children steal from their parents. The sum so ascertained is termed the relatively grave matter. Thus the theft of an amount equal to a day’s wages from an ordinary artisan would unquestionably be a mortal sin. The same thing must be said of the taking of an insignificant sum from a beggar. Theologians teach that this method of establishing the grievousness of theft cannot be employed indefinitely and exclusively. There is an absolute sum which it is always a mortal sin to take even from the wealthiest person or corporation. Were this not so the very fabric of human society would be imperilled, the stimulus to labour and enterprise extinguished, and the axe laid to the root of that confidence which must accompany human intercourse. *
In the attempt to compute this sum in money theologians are not at one; nor is this surprising. In the settlement of the question we have to reckon with a most important factor, that is with the purchasing power of money which is not the same everywhere nor at all times. Writers on economics tell us that for the last hundred years or so this value has decreased from thirty to forty per cent. Of course, the less the value of money at any given time or in any region the more of it would be required to constitute a mortal sin of theft, always, however, within the limits of the principle already laid down. Comparisons instituted between the United States and Europe in the matter of wages prevailing and cost of living, seem to point unmistakably to the conclusion that money has less purchasing capacity here than abroad. Hence where reputable moralists assign as absolutely grave matter, six dollars for Italy, eight for Belgium, and from seven to ten for England, it will not be deemed excessive to fix the amount for this country as ranging from ten to fifteen dollars. One of the greatest of modern theologians, Palmieri, writing in Europe, professes his willingness to stand sponsor for the opinion which makes the sum twenty dollars. He gives as his reason the greatly lessened value of money in our own time. We may not feel obliged to accept this decision, but it is at any rate an indication of the trend of expert opinion.
