When preparing their financial statements of a sole trader’s business for the year ended 31 December 2011, the following accounting adjustments were made:

(i) £16,500 due from a customer was written off as irrecoverable.

(ii) 20% of the cost of vehicles was written off as depreciation.

(iii) An item of inventory costing £6,000 was written down to its realisable value of £4,500.

(iv) School fees paid for the proprietor’s son were debited to the Drawings account.

(v) £2,500 paid for a photocopying machine was written off (instead of being capitalised).

(vi) Insurance paid for the period after the reporting date was transferred to a Prepayments account.

(vii) Cost of inventory in hand at the year-end was determined, as usual, on a first in first out basis.

(viii) A dividend proposed for the year in respect of shares held in a limited company was not accounted for as income because it had not been received.

Required: 

Identify the main accounting concepts on the basis of which the above adjustments were made.