In one form or another, the so-called Linear script of Class A was used in parts of Minoan Crete from the 20th to the middle of the 15th century B.C. It is closely related to two other Cretan scripts, with both of which it overlaps to some extent: an earlier (known as Hieroglyphic or, better, as Pictographic) and a later (known as the Linear script of class B). The precise nature of the interrelationship of these three scripts is not clear. They do not, apparently, descend from one another by a simple process of development. Rather, both Linear A and Linear B seem to have selected elements from a common source, which is either the Pictographic script itself or a system of writing allied to it. The closest similarity between the two classes of Linear script is evident in their external character, that is to say, in the shapes of individual signs: even so, only about half of the signs in the Linear A system have the same shape as those in Linear B. There is much less resemblance in internal character (the structure and function of the scripts). For example, although we find in Linear A many single signs (apparently ideographic or determinative in function) and also sign-groups (which, by reason of the small number employed in all and also by analogy with Linear B practice, are almost certainly phonetic), ideograms are very rarely juxtaposed with phonetic groups, as constantly happens in Linear B. Linear A offers only two certain examples of such juxtaposition, namely in HT 15:1 and 88:4, and even there the order is the reverse of that in Linear B, where the phonetic group regularly precedes the ideogram.