6. It was Dixon J.'s understanding of the concept that is reflected in his Honour's judgment in Carden's Case [1938] HCA 69; (1938) 63 CLR 108 where he said: "If in a given medical practice there is but little certainty about the payment of fees, I should have thought that a receipts basis of accounting would alone reflect truly the income and for most professional incomes it is the more appropriate" (1938) 63 CLR, at p 159 . Thus, in determining whether in such a case actual receipt had to be added to earning in order to find income, uncertainty of receipt, inherent in the circumstances of the earning, appeared to his Honour to be decisive. Likewise, as it seems to us, in determining whether actual earning has to be added to receipt in order to find income, the answer must be given in the light of the necessity for earning which is inherent in the circumstances of the receipt. It is true that in a case like the present the circumstances of the receipt do not prevent the amount received from becoming immediately the beneficial property of the company; for the fact that it has been paid in advance is not enough to affect it with any trust or charge, or to place any legal impediment in the way of the recipient's dealing with it as he will. But those circumstances nevertheless make it surely necessary, as a matter of business good sense, that the recipient should treat each amount of fees received but not yet earned as subject to the contingency that the whole or some part of it may have in effect to be paid back, even if only as damages, should the agreed quid pro quo not be rendered in due course. The possibility of having to make such a payment back (we speak, of course, in practical terms) is an inherent characteristic of the receipt itself. In our opinion it would be out of accord with the realities of the situation to hold, while the possibility remains, that the amount received has the quality of income derived by the company. For that reason it is not surprising to find, as the parties in the present case agree is the fact, that according to established accountancy and commercial principles in the community the books of a business either selling goods or providing services are so kept with respect to amounts received in advance of the goods being sold or of the services being provided that the amounts are not entered to the credit of any revenue account until the sale takes place or the services are rendered: in the meantime they are credited to what is in effect a suspense account, and their transfer to an income account takes place only when the discharge of the obligations for which they are the prepayment justifies their being treated as having finally acquired the character of income. (at p319)