21. This brings me to the final question, namely, whether or not a firm basis can be found for the inclusion amongst the factors to be considered in deciding the proper global sum to be awarded for personal injuries of a figure to reflect the probability of rising costs of the particular goods and services. It can be conceded that in the past over a substantial period of time the purchasing power of the nominal unit of currency in general has declined. Indeed, it may be possible to express that decline in percentage terms of the nominal value of the unit of currency. This decline is not a new experience but an experience of mankind over centuries: but changes in purchasing power have not always been by way of decline nor has the decline been uniform. At times because of particular economic or social conditions in particular places the rate of decline may accelerate, or, for that matter, deceleate, or there may be occasions in the future as there have been in the past when the currency will appreciate. No doubt also there will be periods of greater inflation, such as the present generation has known. So many imponderables must, of course, enter into the causes of these fluctuations; for example, alterations in the mode of production or distribution of the particular community in question or of a representative commodity or commodities of which the cost is taken as a reference point for a general conclusion, or alterations in the social habits of the community creating or diminishing the demand for a commodity. But, notwithstanding these fluctuations, it is possible, by taking a long span of time, that a progressive decline in the purchasing power generally may be demonstrated, though it will not have been regular. But it seems to me that whatever the overall experience in relation to goods and services generally, nothing better in general than a speculation can be made as to the cost in the future of particular goods and services. There is no more room, in my opinion, in the determination of an award of damages, for acting upon a speculation than there is for doing so in the determination of liability. Solid proof, on the basis of probability, is required of all the elements which can properly be reflected in the award. Consequently, in my opinion, evidence which does no more than provide ground for speculation as to the future cost of the required goods and services is inadmissible. (at p550)