Hi Olga: Somewhere along the way in your English studies, you have mistakenly concluded that there is an association or correlation between the 2 words, WHETHER and EITHER, perhaps because the look similar or sound slightly similar. You can understand the meaning of WHETHER by replacing it by other words which can be substituted for WHETHER. Example: "We must check TO SEE IF the partners adhere to our company standards or not." . Or: We must check TO SEE IF "either" of the partners adhere to our company standards or not. EITHER is a distinction between 2 or more things or identities such as People, Places, or Things. WHETHER is a qualification. Example for WHETHER. "I must decide WHETHER or not I should take my vacation in the Winter or the Summer. Example for EITHER, which has an entirely different purpose: I think EITHER of the two persons in the court case is lying to the court. The Liar is EITHER the Defendant or the Plaintiff. or I can paint my room White or Yellow; but EITHER way, it will be much improved. . EITHER, may correspond with NEITHER and you can look that up on the Internet. .