The primary tense in the following paragraphs is the present tense. But I have trouble understanding why the two bolded words (could and would) are in past tense..
There are many misconceptions about the practitioners of chemistry. Many people picture a chemist as a solitary figure who works in a laboratory and does not talk to anyone else for days at a time. Nothing could be further from the truth. Many chemists do indeed work in laboratories but rarely by themselves. A typical day for a modern chemist would be spent as a member of a team solving a particular problem important to his or her company. This team might consist of chemists from various specialties, chemical engineers, development specialists, and possibly even lawyers. Figure 1.1 represents the people and organizations with which typical laboratory chemists might ex- pect to interact in the course of their jobs.
Many topics in economics can be discussed within both a positive and a normative framework. Consider a proposed cut in federal income taxes. An economist practicing positive economics would want to know the effect of a cut in the unemployment rate, economic growth, inflation, and so on. An economist practicing normative economics would address issues that directly or indirectly relate to whether the federal income tax should be cut. For example, she may say that federal income taxes should be cut because the income tax burden on many taxpayer is currently high.