Answer: Without knowing which clematis you have, it is difficult to give you specific advice. There is also in some cases a certain validity to "if it ain't broke, don't fix it" and since the plant was blooming nicely without pruning it may be one of the types that simply doesn't need an annual hard pruning and gets along fine with an occasional tidying of wayward growth.
Many clematis look bare until mid spring when they begin to leaf out, so that a "dead" appearance is not necessarily an indication of future growth, on the other hand last summer was so dry that many clematis did show substantial dieback. They should come back from the roots and remaining vine, however, and any truly dead material can certainly be trimmed away.
Having said that, one of the most common types of dark purple flowered clematis is the "Jackmanii" which flowers in July and August on new growth of the season. This one can be left unpruned, can be pruned moderately to very hard in early spring, or can be pruned to within a foot of the ground, and will come back strong and bloom the same year. When left virtually unpruned, this vine will build up a mass of bare and old stems at the base, so pruning will help it look better by reducing that mass.
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