Taxation is the rule and exemption is the exception. The burden of proof rests upon the party claiming exemption to prove that it is, in fact, covered by the exemption so claimed. As a rule, tax exemptions are construed strongly against the claimant. Exemptions must be shown to exist clearly and categorically, and supported by clear legal provision.
In this case, PAGCOR failed to prove that it is still exempt from the payment of corporate income tax, considering that Section 1 of R.A. No. 9337 amended Section 27 (c) of the National Internal Revenue Code of 1997 by omitting PAGCOR from the exemption. The legislative intent, as shown by the discussions in the Bicameral Conference Meeting, is to require PAGCOR to pay corporate income tax; hence, the omission or removal of PAGCOR from exemption from the payment of corporate income tax. It is a basic precept of statutory construction that the express mention of one person, thing, act, or consequence excludes all others as expressed in the familiar maxim expressio unius est exclusio alterius. Thus, the express mention of the GOCCs exempted from payment of corporate income tax excludes all others. Not being excepted, petitioner PAGCOR must be regarded as coming within the purview of the general rule that GOCCs shall pay corporate income tax, expressed in the maxim: exceptio firmat regulam in casibus non exceptis.