贸易差额基本上记录了一个国家的净出口（出口 – 进口）。贸易差额的恶化或赤字意味着进口的价值超过出口的价值。贸易条件的恶化，一个国家的进口价格指数，可能是由于通货紧缩的货币或财政政策（这将导致G＆S价格普遍下降）等减少支出的措施造成的。价格会下降，而且会相对更贵。假设弹性并且在这些现象中没有发挥重要作用（也许如果两者的弹性总和加起来达到统一或值1），如果增加和减少，贸易差额实际上可能会有所改善。但是，就失去国内就业和产出而言，这可能是不必要的代价。基本上，当一个国家的贸易条件恶化时，相对于出口价格而言变得更加昂贵。假设数量和数量相同，那么当出口价格高于出口时，就会有贸易逆差余额。但是，情况可能不一定如此。贸易差额的结果在很大程度上取决于需求的价格弹性（PED）和出口。 （PED定义为商品需求量变化对价格的变化）当贸易条件恶化时，让我们假设价格上涨和价格下跌。我们假设这是由汇率贬值引起的。如果并且相对有弹性，贸易差额实际上会提高！怎么样？如果价格上涨，需求量将下降相对较大的幅度。这将导致总支出下降。另一方面，当价格下跌时，随之而来的是需求量的相对较大的增加，导致总收入的净增长。结果，将有贸易顺差余额！如果并且相对缺乏弹性，这也适用;导致贸易差额恶化。马歇尔 – 勒纳条件为我们提供了一个简单的规则来评估汇率变化（贸易条款）是否会减少贸易不平衡。它指出，当出口和进口价格弹性的总和大于统一（1）时，汇率（贸易条件）的下降将减少赤字。如果马歇尔 – 勒纳条件成立，当汇率出现贬值时，总收入将增加，总支出将减少。然而，马歇尔 – 勒纳条件只是一个必要条件，并不是汇率下降以改善贸易差额的充分条件。简而言之，马歇尔 – 勒纳条件的出现并不意味着货币贬值必然会改善BOT。为了取得成功，国内产出供应必须能够应对，以应对汇率下降造成的需求激增。需要备用产能以增加供应量，以满足国内和国内对本地生产的替代品的需求。这使我们将使用减少开支的通货紧缩和支出转换贬值作为补充政策而不是替代政策的问题。由于通货紧缩导致实际产出下降，它可能提供备用容量和条件，其中汇率下降可以改善贸易逆差。让我们考虑一个发展中国家孟加拉国，它在渔业中具有比较优势（以比其他国家更低的机会成本生产这种商品或服务）。如果他们的贸易条件恶化，人们可以争辩说，马歇尔 – 勒纳条件对他们有利，因为鱼是蛋白质的弹性来源（可以用鸡肉，牛肉，豆腐等代替），而作为发展中国家，他们的机械，计算机，手机，技术等成品的需求同样具有弹性。但是，鱼的性质是否允许孟加拉国增加供应以满足需求？答案极不可能，因为在某个时间孟加拉国水域只有这么多的鱼。供应的价格弹性，PES（供应到价格变化的数量的响应性）在短期内相对缺乏弹性。除此之外，孟加拉国不会过度捕捞，因为它可能危及其主要收入来源。这不仅会阻碍生产，这可能会改善贸易平衡，但相对于供应增长缓慢而对鱼类的过度需求将推动鱼类价格上涨。
The trade balance basically records the net export (export-import) of a country. A deterioration in the trade balance or a deficit means that the value of imports exceeds the value of exports. The deterioration of terms of trade, a country’s import price index, may be due to measures such as deflationary monetary or fiscal policies (which will lead to a general decline in G&S prices) and other measures to reduce spending. Prices will fall and will be relatively more expensive. It is assumed to be elastic and does not play an important role in these phenomena (perhaps if the sum of the elasticity of the two adds up to a unity or a value of 1), the trade balance may actually improve if it increases and decreases. However, this may be an unnecessary cost in terms of losing domestic employment and output. Basically, when a country’s terms of trade deteriorate, it becomes more expensive relative to export prices. Assuming the same quantity and quantity, then when the export price is higher than the export, there will be a trade deficit balance. However, this may not be the case. The outcome of the trade balance depends to a large extent on the price elasticity of demand (PED) and exports. (PED is defined as the change in demand for goods to price). When the terms of trade deteriorate, let us assume that prices rise and prices fall. We assume that this is caused by the exchange rate depreciation. If and relatively flexible, the trade balance will actually increase! how about it? If the price rises, the demand will fall by a relatively large margin. This will result in a decline in total expenditure. On the other hand, when prices fall, it is followed by a relatively large increase in demand, resulting in a net increase in total income. As a result, there will be a trade surplus balance! This applies if and is relatively inelastic; it leads to a deterioration in the trade balance. Marshall-Lerner conditions provide us with a simple rule to assess whether exchange rate changes (trade terms) will reduce trade imbalances. It pointed out that when the sum of export and import price elasticity is greater than uniform (1), the decline in exchange rate (trade terms) will reduce the deficit. If the Marshall-Lerner condition is established, when the exchange rate depreciates, the total income will increase and the total expenditure will decrease. However, the Marshall-Lerner condition is only a necessary condition and not a sufficient condition for the exchange rate to fall to improve the trade balance. In short, the emergence of Marshall-Lerner conditions does not mean that currency depreciation will inevitably improve BOT. In order to succeed, domestic output supply must be able to cope with the surge in demand caused by falling exchange rates. Alternate capacity is needed to increase supply to meet domestic and domestic demand for locally produced alternatives. This allows us to use the deflation of spending reductions and the devaluation of expenditures as a supplementary policy rather than an alternative policy. As deflation leads to a decline in actual output, it may provide spare capacity and conditions, where a fall in exchange rates can improve the trade deficit. Let us consider a developing country, Bangladesh, which has a comparative advantage in fisheries (production of such goods or services at a lower opportunity cost than other countries). If their terms of trade deteriorate, one can argue that Marshall-Lerner conditions are good for them because fish are an elastic source of protein (which can be replaced with chicken, beef, tofu, etc.), and as a developing country, their machinery, The demand for finished products such as computers, mobile phones, and technology is equally flexible. But does the nature of the fish allow Bangladesh to increase its supply to meet demand? The answer is extremely unlikely, because at some point there are only so many fish in Bangladeshi waters. The price elasticity of supply, PES (the responsiveness of the quantity supplied to the price change) is relatively inelastic in the short term. In addition, Bangladesh does not overfish because it may jeopardize its main source of income. Not only will this hinder production, it may improve the trade balance, but excessive demand for fish relative to slow supply growth will drive fish prices up.