 According to a general approach, minimal pairs are two items that differ in only one feature but have distinct meanings. Take these blue symbols as examples. They all have counterparts where one property, marked red, is changed or added resulting in different meanings. Or look at these Morse code symbols where one dash instead of a dot, whose duration is three times shorter, leads to a different alphabetic symbol and similarly in the system of flag semaphores where different flag positions result in different letters. In phonology, minimal pairs are pairs of words or phrases in a particular language that differ in only one phonological element and have distinct meanings. The phonological elements can be different phonemes, as in present-day English feel versus meal, different tones or tonemes, as in Mandarin Chinese ma versus ma or even different chronemic aspects, that is, length differences, as in German bun versus barn. Let us look at some minimal pairs in present-day English to illustrate phonemic differences. Orthographically, these two word pairs do not seem to be minimal pairs at all. If we look at their phonemic structure, however, they clearly differ in one phoneme and are thus minimal pairs. So it's the phonemic structure that matters, not the orthographical one. The example no versus though once more exemplifies this point. In the 20th century, the setting up of minimal pairs, which goes back to the work of Kenneth Pike, has been used as a major method for the discovery of phonemes in unknown languages.