D.1. The Primacy of Time: Everything exists in a temporal setting, and, in this, decisions about future are the most important ones.
E.1. By proposing that substitution implies either exchange of one with another, or postponing something for the later consumption, it is implied that we are not concerned with a study of statics only. It is now, by the very definition of substitution, true that we are dealing with a scenario where analysis of static conditions alone is not sufficient, and an investigation of dynamics too is our focus – a change in behavior due to change in relative valuation of today's costs and benefits versus tomorrow's benefits and costs etc.
Moreover, since it is now possible to exchange over time, all decisions now essentially take place in a temporal setting. While, ordinarily basic textbooks of Economics do spend a whole lot of time on static analysis, in real life, and also due to this definition of Economics by Robbins, we are concerned not merely with static but essentially with a study of dynamics. However, static analysis does help us understand relative valuations in a simplified setting. Yet, the primacy is of time, and accordingly, the analysis of dynamics dominates the analysis of statics.
E.2. And of what has passed and what has yet to pass, the past bears lesser significance as compared to future. What has happened in past only offers us some information to be used in our analysis but our focus is on what has yet to pass, either by our will or by others, our desired yet unexperienced future is for which all our strife and struggle remains active, and it is also what we wish to predict. Bygones are forever bygones!
Remark: 1.1.2 to 1.1.5 are all observations based on study of full text of essay, and are implicit in essay Robbins, L. (2007). An essay on the nature and significance of economic science. They deserve to be separately mentioned for clarity.