The basic or fundamental principles in accounting are the cost principle, full disclosure principle, matching principle, revenue recognition principle, economic entity assumption, monetary unit assumption, time period assumption, going concern assumption, materiality, and conservatism. The last two are sometimes referred to as constraints. Rather than distinguishing between a principle or an assumption, I prefer to simply say that these ten items are the basic principles or the underlying guidelines of accounting. (My reason is that accounting principles also include the statements of financial accounting standards and the interpretations issued by the Financial Accounting Standards Board and its predecessors, as well as industry practices.)
There are also "qualities" of accounting information such as reliability, relevance, consistency, comparability, and cost/benefit. These are discussed in the Statement of Financial Accounting Concepts No. 2, which can be found on the Financial Accounting Standards Board's website www.FASB.org/st.